Optical diffusion film and method for manufacturing optical diffusion film

ABSTRACT

Disclosed is an optical diffusion film having, inside the film, a single optical diffusion layer having a first internal structure and a second internal structure, each of which include a plurality of regions having a relatively high refractive index in a region having a relatively low refractive index, sequentially from the lower part along the film thickness direction, and the regions having a relatively high refractive index in the first internal structure have a bent section at an intermediate point along the film thickness direction.

This application is a continuation application of U.S. National-Stageapplication Ser. No. 15/513,059 filed on Mar. 21, 2017, which claims thebenefit of PCT/JP2014/076321 filed on Oct. 1, 2014.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to an optical diffusion film and a methodfor manufacturing an optical diffusion film.

More particularly, the invention relates to an optical diffusion filmcomposed of a single layer, for which the optical diffusion incidentangle region can be effectively expanded, and even in a case in whichthe incident angle of incident light is varied within the opticaldiffusion incident angle region, changes in the optical diffusioncharacteristics can be effectively suppressed, and to a method formanufacturing an optical diffusion film.

2. Description of the Related Art

In the field of optical technology to which, for example, liquid crystaldisplay devices and the like belong, optical diffusion films that candiffuse an incident light coming from a particular direction intoparticular directions, while transmitting straight an incident lightcoming from any other directions, have been conventionally used.

Various forms of such optical diffusion films are known; however, inparticular, optical diffusion films having, within the films, a louverstructure in which a plurality of plate-shaped regions having differentrefractive indices are alternately arranged in one arbitrary directionalong the film plane, have been widely used.

Furthermore, regarding optical diffusion films of another type, opticaldiffusion films having, within the film, a columnar structure in which aplurality of pillar-shaped objects having a relatively high refractiveindex are arranged to stand close together in a region having arelatively low refractive index, have also been widely used.

However, when an optical diffusion film only has a louver structurehaving a single inclination angle or a columnar structure within thefilm, there is a problem that a sufficient optical diffusion incidentangle region may not be obtained.

Thus, there has been suggested a technology of expanding the opticaldiffusion incident angle region by regulating the conditions employedwhen an internal structure is formed by irradiating a composition for anoptical diffusion film with active energy radiation, and thereby curvingthe entirety of the internal structure in the film thickness directionor providing a bent section in the internal structure (see, for example,JP 2006-323379 Å and JP 2013-195672 Å).

Meanwhile, the term “optical diffusion incident angle region” means therange of the angle of incidence through which diffused light can beemitted when the angle of incidence of incident light coming from apoint light source is changed in an optical diffusion film.

Namely, JP 2006-323379 A discloses a method for manufacturing a lightcontrol film (optical diffusion film), by which a film-like composition(composition for an optical diffusion film) that contains at least twokinds of compounds each having a polymerizable carbon-carbon bond in themolecule and having mutually different refractive indices, is irradiatedwith ultraviolet radiation through an interference filter having atransmittance of 0% to 60% to light having a wavelength of 313 nm, andthe composition is cured.

Furthermore, as illustrated in FIGS. 21(a) and 21(b), regarding a lightcontrol film 207 manufactured by the method described above, a lightcontrol film 207 in which the difference (α_(a)−α_(b)) between theminimum angle of inclination α_(a) and the maximum angle of inclinationα_(b) in a cross-section of the light control film 207 observed by anoptical microscope, has been disclosed.

JP 2013-195672 A discloses an anisotropic optical film (opticaldiffusion film) 353 having, as illustrated in FIG. 22, at least lowrefractive index regions (341, 342, and 343) and a high refractive indexregion 306 inside a single anisotropic diffusion layer 307, theanisotropic optical film having a structure in which at the surface ofthe single anisotropic diffusion layer 307, the low refractive indexregions (341 and 343) and the high refractive index region 306 arealternately aligned; in a cross-section of the single anisotropicdiffusion layer 307, the low refractive index regions (341, 342, and343) and the high refractive index region (306) exist in the form ofbeing bent in the thickness direction; the anisotropic optical film hasa first diffusion central axis in the upper part 371 of the singleanisotropic diffusion layer 307, and has a second diffusion central axisin the medium part 372 of the single anisotropic diffusion layer; andthe gradient of the first diffusion central axis and the gradient of thesecond diffusion central axis with respect to the normal direction aredifferent.

Furthermore, as a method of forming a bent internal structure, a methodof irradiating a photocurable composition layer (layer formed from acomposition for an optical diffusion film) with ultraviolet radiation,while applying a temperature distribution in the thickness direction ofthe photocurable composition layer, has been disclosed.

JP 2013-195672 A also discloses, as illustrated in FIG. 22, anembodiment having a third diffusion central axis in the lower part 373of the single anisotropic diffusion layer 307, that is, an embodimenthaving two bent sections in the internal structure.

On the other hand, there has been suggested a technology of irradiatinga composition for an optical diffusion film with active energy radiationin two stages, thereby forming two internal structures in sequence fromthe lower part along the film thickness direction, and expanding theoptical diffusion incident angle region (see, for example, JP2012-141593 A and WO 2013/108540 A).

Namely, JP 2012-141593 A discloses an optical diffusion film 430 having,as illustrated in FIGS. 23(a) and 23(b), a first structural region 410for anisotropically diffusing incident light, and a second structuralregion 420 for isotropically diffusing incident light, characterized inthat the first structural region 410 is a louver structural region inwhich a plurality of plate-shaped regions having different refractiveindices are alternately arranged in parallel along the film planedirection, and the second structural region is a columnar structuralregion in which a plurality of pillar-shaped objects are arranged tostand close together in a medium, the pillar-shaped objects having arefractive index different from that of the medium.

Furthermore, WO 2013/108540 A discloses an anisotropic optical diffusionfilm 540 having, as illustrated in FIGS. 24(a) and 24(b), a first louverstructural region 520 and a second louver structural region 530, in eachof which a plurality of plate-shaped regions having different refractiveindices are alternately arranged in parallel along any one directionalong the film plane, sequentially from the lower part along the filmthickness direction, characterized in that the anisotropic opticaldiffusion film 540 has an overlapping louver structural region in whichthe position of the upper end of the first louver structural region 520and the position of the lower end of the second louver structural region530 overlap each other in the film thickness direction.

SUMMARY OF THE INVENTION

However, the optical diffusion film described in JP 2006-323379 A has aproblem that the degree of freedom in the control of curvature is low,and it is difficult to sufficiently expand the optical diffusionincident angle region.

Furthermore, there is a problem that stability in the control ofcurvature is also low, and it is difficult to curve the internalstructure stably at a desired angle.

There is also another problem that on the occasion of curving theinternal structure, when the composition for an optical diffusion filmis irradiated with ultraviolet radiation, a very expensive interferencefilter such as a band pass filter must be used, and it is economicallydisadvantageous.

The optical diffusion film described in JP 2013-195672 A also has aproblem that the degree of freedom in control of the bent section islow, and it is difficult to sufficiently expand the optical diffusionincident angle region.

The optical diffusion film described in JP 2013-195672 A also has aproblem that the degree of freedom in control of the bent section islow, and it is difficult to sufficiently expand the optical diffusionincident angle region.

Also, in JP 2013-195672 A, since a bent section is formed by irradiatinga composition for an optical diffusion film with ultraviolet radiationwhile applying a temperature distribution, there is a problem thatstability in the control of the section is very low, and it is difficultto bend the internal structure stably at a desired angle.

Meanwhile, the optical diffusion films described in JP 2012-141593 A andWO 2013/108540 A are configured such that two internal structures areseparately formed. Therefore, the degree of freedom in control of therespective angles of inclination of the internal structures is high, andthe optical diffusion incident angle region can be expanded to a certainextent.

However, in a case in which the optical diffusion incident angle regionis expanded to a predetermined extent, or even more, a phenomenon mayoccur, in which it is speculated that depending on the incident angle ofincident light, the light that has been diffused by the first internalstructure may become almost undiffusible by the second internalstructure, or the light that could not be diffuse by the first internalstructure is diffused only by the second internal structure.

Therefore, despite that the incident angle of incident light is variedwithin the optical diffusion incident angle region, the opticaldiffusion characteristics may change.

As a countermeasure for this problem, an embodiment of increasing theregion in which the optical diffusion incident angle region provided bythe first internal structure overlaps with the optical diffusionincident angle region provided by the second internal structure, may bementioned. However, in that case, the degree of freedom for the anglesof inclination of the internal structures, or the overall opticaldiffusion incident angle region of the film provided by the two internalstructures becomes narrower.

Thus, the inventors of the present invention conducted a thoroughinvestigation in view of such circumstances as described above, and theinventors found that when a bent section is provided at least in aregion having a relatively high refractive index, which constitutes afirst internal structure, the optical diffusion incident angle regioncan be effectively expanded, and also, even in a case in which theincident angle of incident light is varied within the optical diffusionincident angle region, changes in the optical diffusion characteristicscan be effectively suppressed. Thus, the inventors completed the presentinvention.

An object of the invention is to provide an optical diffusion filmcomposed of a single layer, for which the optical diffusion incidentangle region can be effectively expanded, and even when the incidentangle of incident light is varied within the optical diffusion incidentangle region, changes in the optical diffusion characteristics can beeffectively suppressed; and a method for manufacturing the opticaldiffusion film.

According to an aspect of the invention, there is provided an opticaldiffusion film having, inside the film, a single optical diffusion layerhaving a first internal structure and a second internal structure, eachof which includes a plurality of regions having a relatively highrefractive index (hereinafter, may be referred to as “high refractiveindex region”) in a region having a relatively low refractive index(hereinafter, may be referred to as “low refractive index region”),sequentially from the lower part along the film thickness direction, inwhich the regions having a relatively high refractive index in the firstinternal structure each have a bent section at an intermediate pointalong the film thickness direction. Thus, the problems described abovecan be solved.

That is, when the optical diffusion film of the invention is used, sincethe film has a first internal structure and a second internal structureinside the film, and a bent section is provided at least in the regionshaving a relatively high refractive index that constitute the firstinternal structure, two optical diffusion incident angle regionsoriginating from the first internal structure and at least one opticaldiffusion incident angle region originating from the second internalstructure can be stably obtained.

Therefore, when altogether three optical diffusion incident angleregions are superposed while being shifted in an appropriate range, theoverall optical diffusion incident angle region of the film can beeffectively expanded.

Furthermore, since incident light can be gradually diffused in threestages, compared to a case in which incident light is diffused bydiffusion in two stages, even in a case in which the overall opticaldiffusion incident angle region of the film is expanded to the sameextent, the changes in the optical diffusion characteristics associatedwith variation in the incident angle of incident light can beeffectively suppressed.

Furthermore, since the optical diffusion film is composed of a singlelayer, compared to a case in which a plurality of optical diffusionfilms are laminated, not only it is economically advantageous becausethe processes of layer bonding can be reduced, but the occurrence ofblurring in displayed images or the occurrence of delamination can alsobe effectively suppressed.

The term “single layer” means that a plural number of optical diffusionfilms are not laminated.

The term “intermediate point” means a center point with respect to twoedges, as well as any one arbitrary point in the middle between the twoedges.

Furthermore, on the occasion of configuring the optical diffusion filmof the invention, it is preferable to have an overlapping internalstructure in which the position of the upper end of the first internalstructure and the position of the lower end of the second internalstructure overlap with each other in the film thickness direction.

When the optical diffusion film is configured as such, generation ofscattered light can be effectively suppressed, and uniformity of theintensity of diffused light can be enhanced, compared to a case in whicha portion where an internal structure is not formed exists between therespective internal structures.

On the occasion of configuring the optical diffusion film of theinvention, it is preferable that the overlapping internal structure isan overlapping internal structure in which the tips of the regionshaving a relatively high refractive index, which originate from any oneof the first internal structure and the second internal structure, arein contact with the vicinity of the tips of the regions having arelatively high refractive index, which originate from the otherinternal structure; or an overlapping internal structure in which theregions having a relatively high refractive index, which respectivelyoriginate from the first internal structure and the second internalstructure, overlap in a non-contact state.

When the optical diffusion film is configured as such, internalstructures can be efficiently disposed within the limited filmthickness, generation of scattered light can be more effectivelysuppressed, and uniformity of the intensity of diffused light can beenhanced.

Furthermore, on the occasion of configuring the optical diffusion filmof the invention, it is preferable that the thickness of the overlappinginternal structure is adjusted to a value within the range of 1 to 40μm.

When the optical diffusion film is configured as such, generation ofscattered light in the overlapping internal structure can be moreeffectively suppressed, and uniformity of the intensity of diffusedlight can be enhanced.

On the occasion of configuring the optical diffusion film of theinvention, it is preferable that with regard to the overlapping internalstructure, the absolute value of the difference of the angles ofinclination of the regions having a relatively high refractive index,which respectively originate from the first internal structure and thesecond internal structure, is adjusted to a value of 1° or more.

When the optical diffusion film is configured as such, the opticaldiffusion incident angle region can be more effectively expanded.

On the occasion of configuring the optical diffusion film of theinvention, it is preferable that in the first internal structure, theangle of inclination θa, with respect to the normal line of the filmplane, of the regions having a relatively high refractive index in theportion upper than the bent section is adjusted to a value within therange of 0° to 30°, and the angle of inclination θb, with respect to thenormal line of the film plane, of the regions having a relatively highrefractive index in the portion lower than the bent section is adjustedto a value within the range of 1° to 60°.

When the optical diffusion film is configured as such, the opticaldiffusion incident angle region can be more effectively expanded.

The “portion upper than the bent section” means the portion on the sidethat is irradiated with active energy radiation when the opticaldiffusion film is manufactured, with respect to the bent section as areference, and the “portion lower than the bent section” means theportion on the opposite side with respect to the bent section as areference.

Furthermore, on the occasion of constituting the optical diffusion filmof the invention, it is preferable that in the first internal structure,the length La of the regions having a relatively high refractive indexin the portion upper than the bent section is adjusted to a value withinthe range of 15 to 475 μm, and the length Lb of the regions having arelatively high refractive index in the portion lower than the bentsection is adjusted to a value within the range of 15 to 475 μm.

When the optical diffusion film is configured as such, changes in theoptical diffusion characteristics associated with variation in theincident angle of incident light can be effectively suppressed, whilethe optical diffusion incident angle region can be more effectivelyexpanded.

On the occasion of configuring the optical diffusion film of theinvention, it is preferable that the first internal structure is acolumnar structure in which a plurality of pillar-shaped regions havinga relatively high refractive index are arranged to stand close togetherin the film thickness direction in a region having a relatively lowrefractive index, or a louver structure in which a plurality ofplate-shaped regions having different refractive indices are alternatelydisposed in one arbitrary direction along the film plane.

When the optical diffusion film is configured as such, a distinct firstinternal structure having a predetermined difference in refractive indexcan be formed, and a bent section can be definitely provided in theregion having a relatively high refractive index.

Furthermore, on the occasion of configuring the optical diffusion filmof the invention, it is preferable that the second internal structure isa columnar structure in which a plurality of pillar-shaped regionshaving a relatively high refractive index are arranged to stand closetogether in the film thickness direction in a region having a relativelylow refractive index, or a louver structure in which a plurality ofplate-shaped regions having different refractive indices are alternatelydisposed in one arbitrary direction along the film plane.

When the optical diffusion film is configured as such, a distinct secondinternal structure having a predetermined difference in refractive indexcan be formed.

According to another aspect of the invention, there is provided a methodfor manufacturing the optical diffusion film described above, the methodincluding the following steps (a) to (d):

(a) a step of preparing a composition for an optical diffusion film, thecomposition including at least two polymerizable compounds havingdifferent refractive indices, a photopolymerization initiator and anultraviolet absorber, in which the content of the ultraviolet absorberis adjusted to a value of below 2 parts by weight (provided that 0 partsby weight is excluded) with respect to the total amount (100 parts byweight) of the at least two polymerizable compounds having differentrefractive indices;

(b) a step of applying the composition for an optical diffusion film ona process sheet, and forming a coating layer;

(c) a step of performing first irradiation of the coating layer withactive energy radiation, forming a first internal structure in the lowerportion of the coating layer, and also leaving a region where aninternal structure is not formed, in the upper portion of the coatinglayer; and

(d) a step of performing second irradiation of the coating layer withactive energy radiation, and forming a second internal structure in theregion where an internal structure is not formed.

That is, when the method for manufacturing an optical diffusion film ofthe invention is used, since the composition for an optical diffusionfilm includes a predetermined amount of an ultraviolet absorber, a bentsection can be provided stably in the regions having a relatively highrefractive index that constitute the first internal structure, by thefirst irradiation with active energy radiation.

Furthermore, since a coating layer formed from a predeterminedcomposition for an optical diffusion film is subjected to first andsecond irradiation with active energy radiation, the combination of theangles of inclination of the regions having a relatively high refractiveindex in the first and second internal structures can be regulatedeasily by appropriately regulating the angle of irradiation for theirradiation with active energy radiation.

Also, since the first and second internal structures are formed within asingle layer, the occurrence of delamination in the optical diffusionfilm thus obtained can be fundamentally suppressed.

On the occasion of implementing the method for manufacturing an opticaldiffusion film of the invention, it is preferable that the firstirradiation with active energy radiation is performed in anoxygen-containing atmosphere, and the second irradiation with activeenergy radiation is performed in a non-oxygen atmosphere.

When the method is carried out as such, the first internal structure canbe efficiently formed in the lower portion of the coating layer, while aregion where an internal structure is not formed can be caused to stablyremain in the upper portion of the coating layer by utilizing the effectof oxygen inhibition.

On the other hand, in the region where an internal structure is notformed, a second internal structure can be efficiently formed bysuppressing the effect of oxygen inhibition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and 1(b) are diagrams provided to explain the configurationof the optical diffusion film of the invention.

FIG. 2 is a diagram provided to explain the optical diffusioncharacteristics of the optical diffusion film of the invention.

FIG. 3 is a diagram provided to explain the optical diffusioncharacteristics of a conventional optical diffusion film.

FIGS. 4(a) and 4(b) are diagrams provided to explain an embodiment ofthe optical diffusion film of the invention.

FIGS. 5(a) and 5(b) are diagrams provided to explain an embodiment ofthe overlapping internal structure.

FIGS. 6(a) to 6(c) are diagrams provided to explain the method formanufacturing an optical diffusion film of the invention.

FIG. 7 is a diagram provided to explain the angle of irradiation withactive energy radiation.

FIGS. 8(a) and 8(b) are a schematic diagram and a photograph of across-section in the optical diffusion film of Example 1.

FIGS. 9(a) and 9(b) are diagrams provided to explain the angle ofincidence θ2 with respect to the optical diffusion film when opticaldiffusion characteristics are measured.

FIGS. 10(a) to 10(g) are diagrams provided to explain the opticaldiffusion characteristics in the optical diffusion film of Example 1.

FIGS. 11(a) and 11(b) are a schematic diagram and a photograph of across-section in the optical diffusion film of Example 2.

FIGS. 12(a) to 12(g) are diagrams provided to explain the opticaldiffusion characteristics of the optical diffusion film of Example 2.

FIGS. 13(a) and 13(b) are a schematic diagram and a photograph of across-section in the optical diffusion film of Example 3.

FIGS. 14(a) to 14(g) are diagrams provided to explain the opticaldiffusion characteristics of the optical diffusion film of Example 3.

FIGS. 15(a) and 15(b) are a schematic diagram and a photograph of across-section of the optical diffusion film of Comparative Example 1.

FIGS. 16(a) to 16(g) are diagrams provided to explain the opticaldiffusion characteristics of the optical diffusion film of ComparativeExample 1.

FIGS. 17(a) and 17(b) are a schematic diagram and a photograph of across-section of the optical diffusion film of Comparative Example 2.

FIGS. 18(a) to 18(g) are diagrams provided to explain the opticaldiffusion characteristics of the optical diffusion film of ComparativeExample 2.

FIGS. 19(a) and 19(b) are a schematic diagram and a photograph of across-section of the optical diffusion film of Comparative Example 3.

FIGS. 20(a) to 20(g) are diagrams provided to explain the opticaldiffusion characteristics of the optical diffusion film of ComparativeExample 3.

FIGS. 21(a) and 21(b) are diagrams provided to explain a conventionaloptical diffusion film.

FIG. 22 is another diagram provided to explain a conventional opticaldiffusion film.

FIGS. 23(a) and 23(b) are still other diagrams provided to explain aconventional optical diffusion film.

FIGS. 24(a) and 24(b) are still other diagrams provided to explain aconventional optical diffusion film.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

A first embodiment of the present invention relates to an opticaldiffusion film having a single optical diffusion layer having a firstinternal structure and a second internal structure, both of whichinclude a plurality of regions having a relatively high refractive indexin a region having a relatively low refractive index, sequentially fromthe lower part along the film thickness direction, in which the regionshaving a relatively high refractive index in the first internalstructure have a bent section at an intermediate point along the filmthickness direction.

Hereinafter, the first embodiment of the invention will be specificallydescribed with appropriate reference to the drawings.

1. Basic Configuration

First, the basic configuration of the optical diffusion film 10 of theinvention will be specifically described using FIGS. 1(a) and 1(b), bytaking a case in which the first internal structure 20 and the secondinternal structure 30 are both columnar structures (20 a and 30 a) as anexample.

Here, FIG. 1(a) shows a perspective view illustrating the entirety ofthe optical diffusion film 10, and FIG. 1(b) shows a cross-sectionalview of the optical diffusion film 10 of FIG. 1(a).

However, FIG. 1(b) is used as a comprehensive diagram that is notlimited to a case in which the first and second internal structures (20,30) are both columnar structures (20 a, 30 a), but also includes a casein which, for example, the internal structures are other internalstructures such as a louver structure.

As illustrated in such FIGS. 1(a) and 1(b), the optical diffusion film10 is a film 10 having a single optical diffusion layer 50 having afirst columnar structure 20 a and a second columnar structure 30 a, bothof which include pillar-shaped objects (12 a, 12 a′) as a plurality ofregions having a relatively high refractive index (12, 12′) in a region11 having a relatively low refractive index, sequentially from the lowerpart along the film thickness direction.

Furthermore, the pillar-shaped objects 12 a in the first columnarstructure 20 a have a bent section 14 at an intermediate point along thefilm thickness direction.

2. Optical Diffusion Characteristics

Next, the optical diffusion characteristics of the optical diffusionfilm 10 of the invention will be specifically described using FIG. 2, bytaking a case in which the first internal structure 20 and the secondinternal structure 30 are both columnar structures (20 a, 30 a) as anexample.

Here, FIG. 2 shows a perspective view of the optical diffusion film 10.

As illustrated in such FIG. 2, the optical diffusion film 10 has a firstcolumnar structure 20 a and a second columnar structure 30 a in thefilm, and is also provided with a bent section 14 in the pillar-shapedobjects that constitute the first columnar structure 20 a.

Therefore, as illustrated in FIG. 2, the overall optical diffusionincident angle region of the film can be effectively expanded bysuperposing three optical diffusion incident angle regions attributableto the first columnar structure 20 a and the second columnar structure30 a while shifting the optical diffusion incident angle regions in anappropriate range.

Here, in a columnar structure, incident light coming at an incidentangle that is approximately parallel to the angle of inclination of thepillar-shaped objects constituting the columnar structure, can beefficiently diffused without any loss. This is because such an incidentangle is included in the optical diffusion incident angle region.

However, with regard to incident light coming at an incident angle thatperfectly coincides with the angle of inclination of the pillar-shapedobjects, the columnar structure may transmit the incident light withoutsufficiently diffusing it.

In this regard, the optical diffusion film 10 of the invention caneffectively solve this problem.

For instance, as in the case of incident light represented by arrow A,incident light coming at an incident angle that is perfectly parallel tothe angle of inclination of the pillar-shaped objects of the secondcolumnar structure 30 a tends to be not sufficiently diffused by thesecond columnar structure 30 a. However, the optical diffusion film 10illustrated in FIG. 2 gradually diffuses incident light in two stages bymeans of the first columnar structure 20 a composed of pillar-shapedobjects having a bent section 14, and can finally diffuse the incidentlight at a sufficient level.

Furthermore, for example, as in the case of incident light representedby arrow B, incident light coming at an incident angle that issignificantly different from the angle of inclination of thepillar-shaped objects of the second columnar structure 30 a, is merelydiffused into a crescent shape by means of the lateral faces of thepillar-shaped objects of the second columnar structure 30 a, andtherefore, the incident light tends to be diffused insufficiently in thestage of the second columnar structure 30 a. However, the opticaldiffusion film 10 illustrated in FIG. 2 can finally diffuse the incidentlight at a sufficient level by means of the first columnar structure 20a that is composed of the pillar-shaped objects having a bent section14.

Therefore, the optical diffusion film of the invention can effectivelysuppress the changes in the optical diffusion characteristics associatedwith variation in the incident angle of incident light, while having theoverall optical diffusion incident angle region of the film effectivelyexpanded.

Meanwhile, even in a case in which incident light is diffused in twostages as illustrated in FIG. 3, the overall optical diffusion incidentangle region of the film can be expanded.

However, there are occasions in which when it is attempted to expand theoptical diffusion incident angle region to the same extent as that ofthe optical diffusion film 10 of the invention, the angles ofinclination of the pillar-shaped objects of the first columnar structure20 and the pillar-shaped objects of the second columnar structure 30must be made significantly different. In this case, it may be difficultto effectively suppress the changes in the optical diffusioncharacteristics associated with variation in the incident angle ofincident light.

For example, in an optical diffusion 10′ illustrate in FIG. 3, incidentlight coming at an incident angle that is perfectly parallel to theangle of inclination of the pillar-shaped objects of the second columnarstructure 30, such as incident light represented by the arrow A, may notbe sufficiently diffused by the second columnar structure 30. Then, whensuch insufficiently diffused light penetrates into the first columnarstructure at an incident angle that is significantly different from theangle of inclination of the pillar-shaped objects of the first columnarstructure 20, the diffused light may not be efficiently guided into thepillar-shaped objects of the first columnar structure 20, and may not befinally diffused at a sufficient level.

Furthermore, for example, incident light coming at an incident anglethat is significantly different from the angle of inclination of thepillar-shaped objects of the second columnar structure 30, such asincident light represented by the arrow B, is merely diffused in acrescent shape by the lateral faces of the pillar-shaped objects of thesecond columnar structure 30, and therefore, the incident light tends tobe diffused insufficiently. In the case of the optical diffusion film10′ illustrated in FIG. 3, since the first columnar structure 20 iscomposed of pillar-shaped objects that do not have a bent section, thelight that has been insufficiently diffused by the second columnarstructure 30 may not be efficiently guided into the pillar-shapedobjects of the first columnar structure 20, and the diffused light maynot be finally diffused at a sufficient level.

Furthermore, when the angles of inclination of the first and secondcolumnar structures are adjusted to be close to each other in order toimprove such optical diffusion characteristics, the optical diffusionincident angle region becomes narrow.

Therefore, in the case of a conventional optical diffusion film of thetype that diffuses light in two stages, the overall incident angleregion of the film can be effectively expanded; however, it may bedifficult to suppress any changes in the optical diffusioncharacteristics associated with variation in the incident angle ofincident light.

The invention has been explained by taking a case in which incidentlight enters through the second columnar structure side as an example;however, the same also applies to a case in which incident light entersthrough the first columnar structure side.

Furthermore, diffusion in three stages has been explained as an example;however, the diffusion may also be diffusion in four or more stages.

In regard to the optical diffusion film of the invention, the inventionhas been explained by taking a case in which the first and secondinternal structures are both columnar structures as an example; however,there are no particular limitations on the first and second internalstructures.

Specifically, an embodiment as illustrated in FIG. 4(a), in which thefirst and second internal structures are both louver structures (20 b,30 b); an embodiment as illustrated in FIG. 4(b), in which the firstinternal structure is a louver structure 20 b, while the second internalstructure is a columnar structure 30 a; and an embodiment in which thefirst internal structure is a columnar structure 20 a, while the secondinternal structure is a louver structure 30 b, may be mentioned.

There is a difference between a columnar structure and a louverstructure that the columnar structure induces isotropic opticaldiffusion of incident light (optical diffusion by which the planar shapeof diffused light becomes approximately circular), whereas the louverstructure induces anisotropic optical diffusion of incident light(optical diffusion by which the planar shape of diffused light islinear).

Furthermore, it is speculated that optical diffusion by a columnarstructure or a louver structure is achieved when light entering into aregion having a relatively high refractive index, such as apillar-shaped objects or a plate-shaped region in the respectivestructures, escapes the film while repeatedly undergoing reflection atthe interface between the region having a relatively high refractiveindex and a region having a relatively low refractive index.

3. First Internal Structure

The first internal structure in the optical diffusion film of theinvention is not particularly limited as long as it is a structureincluding a plurality of regions having a relatively high refractiveindex in a region having a relatively low refractive index; however, thefirst internal structure is characterized in that the regions having arelatively high refractive index has a bent section at an intermediatepoint along the film thickness direction.

In the following description, a bent columnar structure and a bentlouver structure will be explained as examples.

(1) Bent Columnar Structure

As illustrated in FIG. 1(a), it is preferable that the first internalstructure is a columnar structure 20 a in which a plurality ofpillar-shaped objects 12 a having a relatively high refractive index arearranged to stand close together in the film thickness direction in aregion 11 having a relatively low refractive index, the pillar-shapedobjects 12 a having a bent section 14 at an intermediate point along thefilm thickness direction.

The reason for this is that when such a bent columnar structure isemployed, a distinct first internal structure having a predetermineddifference in refractive index can be formed, and also, a bent sectioncan be definitely provided in a region having a relatively highrefractive index.

Hereinafter, the bent columnar structure will be specifically described.

(1)-1 Refractive Index

In regard to the bent columnar structure, it is preferable that thedifference between the refractive index of the pillar-shaped objectshaving a relatively high refractive index and the refractive index ofthe region having a relatively low refractive index is adjusted to avalue of 0.01 or more.

The reason for this is that if the difference in refractive index assuch has a value of below 0.01, the range of angle at which incidentlight is fully reflected within the bent columnar structure becomesnarrow, and thus, the incident angle dependency may be excessivelydecreased.

Therefore, it is more preferable that the difference in refractive indexis adjusted to a value of 0.05 or more, and even more preferably to avalue of 0.1 or more.

It is more preferable as the difference in refractive index is larger;however, from the viewpoint of selecting a material capable of forming abent columnar structure, it is considered that the upper limit is about0.3.

The term “incident angle dependency” means a characteristic that enablesclear distinction between the incident angle region of incident light inwhich incident light is diffused, and the incident angle region ofincident light in which incident light is not diffused.

(1)-2 Maximum Diameter and Interval

In regard to the bent columnar structure 20 a illustrated in FIG. 1(a),it is preferable that the maximum diameter in a cross-section of apillar-shaped object 12 a and the interval between the pillar-shapedobjects 12 a are respectively adjusted to a value within the range of0.1 to 15 μm.

The reason for this is that if the maximum diameter and the intervalrespectively have a value of below 0.1 μm, it may be difficult for theoptical diffusion film to exhibit optical diffusion characteristics,regardless of the incident angle of incident light. On the other hand,it is because if the maximum diameter and the interval respectively havea value of above 15 μm, the amount of light propagating straight throughthe bent columnar structure increases, and uniformity of opticaldiffusion may be deteriorated.

Therefore, in regard to the bent columnar structure, it is morepreferable that the maximum diameter and the interval are respectivelyset to a value of 0.5 μm or more, and even more preferably to a value of1 μm or more.

Furthermore, in regard to the bent columnar structure, it is morepreferable that the maximum diameter and the interval are respectivelyset to a value of 10 μm or less, and even more preferably to a value of5 μm or less.

The cross-sectional shape of the pillar-shaped object is notparticularly limited; however, it is preferable to make thecross-sectional shape into, for example, a circular shape, an ellipticalshape, a polygonal shape, or an irregular shape.

The cross-section of a pillar-shaped object means a cross-sectionobtained by cutting the pillar-shaped object along a plane parallel tothe film surface.

Furthermore, the maximum diameter, length and the like of apillar-shaped object can be calculated by making an observation with anoptical digital microscope.

(1)-3 Thickness

It is preferable that the thickness (length in the film thicknessdirection) of the bent columnar structure 20 a illustrated in FIG. 1(a),that is, the length L1 in FIG. 1(b), is adjusted to a value within therange of 30 to 500 μm.

The reason for this is that if the length L1 has a value of below 30 μm,the amount of light propagating straight through the bent columnarstructure increases, and it may be difficult to obtain sufficientincident angle dependency and a sufficient optical diffusion incidentangle region. On the other hand, it is because if the length L1 has avalue of above 500 μm, when a bent columnar structure is formed byirradiating a composition for an optical diffusion film with activeenergy radiation, the direction of progress of photopolymerization isdiffused by the columnar structure that has been initially formed, andit may be difficult to form a desired bent columnar structure.

Therefore, it is more preferable that the length L1 of the bent columnarstructure is adjusted to a value of 50 μm or more, and even morepreferably to a value of 70 μm or more.

It is also more preferable that the length L1 of the bent columnarstructure is adjusted to a value of 325 μm or less, and even morepreferably to a value of 200 μm or less.

Furthermore, in the bent columnar structure 20 a illustrated in FIG.1(a), it is preferable that the length in the film thickness directionof the pillar-shaped objects 12 a in the portion upper than the bentsection 14 (portion on the side that is irradiated with active energyradiation when the optical diffusion film is manufactured, with respectto the bent section as a reference), that is, the length La in FIG.1(b), is adjusted to a value within the range of 15 to 475 μm.

The reason for this is that if the length La has a value of below 15 μm,diffusion induced by the columnar structure in the upper portion becomestoo weak, and it may be difficult to effectively expand the opticaldiffusion incident angle region. Meanwhile, as the content of anultraviolet absorber in the composition for an optical diffusion film islarger, the length tends to become shorter. Therefore, in other words,when it is said that the length is excessively short, the content of theultraviolet absorber becomes very large, and in that case, when acomposition for an optical diffusion film is photocured, the possibilityof generation of shrinkage wrinkles in the film is increased, andcontrol is difficult.

On the other hand, if the length La has a value of above 475 μm, thecontent of the ultraviolet absorber becomes very small, and in thatcase, the columnar structure in the lower portion is not sufficientlyformed, and there is a possibility that it may be difficult toeffectively expand the optical diffusion incident angle region.

Therefore, it is more preferable that the length La of the pillar-shapedobjects in the portion upper than the bent section in the bent columnarstructure is adjusted to a value of 25 μm or more, and even morepreferably to a value of 30 μm or more.

Furthermore, it is more preferable that the length La of thepillar-shaped objects in the portion upper than the bent section in thebent columnar structure is adjusted to a value of 300 μm or less, andeven more preferably to a value of 150 μm or less.

It is also preferable that the length in the film thickness direction ofthe pillar-shaped objects 12 a in the portion lower than the bentsection 14 (portion on the opposite side of the above-mentioned upperportion with respect to the bent section as a reference) in the bentcolumnar structure 20 a illustrated in FIG. 1(a), that is, the length Lbin FIG. 1(b), is adjusted to a value within the range of 15 to 475 μm.

The reason for this is that if the length Lb has a value of below 15 μm,diffusion originating from the columnar structure in the lower portionbecomes so weak that it may be difficult to effectively expand theoptical diffusion incident angle region. On the other hand, it isbecause if the length Lb has a value of above 475 μm, although diffusionoriginating from the columnar structure of the lower portion can besufficiently obtained, the film thickness of the optical diffusion filmbecomes excessively thick, and application of the optical diffusion filmfor display use may be infeasible.

Accordingly, it is more preferable that the length Lb of thepillar-shaped objects in the portion lower than the bent section in thebent columnar structure is adjusted to a value of 25 μm or more, andeven more preferably to a value of 30 μm or more.

Furthermore, it is more preferable that the length Lb of thepillar-shaped objects in the portion lower than the bent section in thebent columnar structure is adjusted to a value of 300 μm or less, andeven more preferably to a value of 150 μm or less.

(1)-4 Angle of Inclination

In regard to the bent columnar structure 20 a illustrated in FIG. 1(a),it is preferable that the pillar-shaped objects 12 a as the regions 12having a relatively high refractive index (hereinafter, may be referredto as highly refractive regions) are arranged in parallel at a constantangle of inclination in the film thickness direction.

The reason for this is that when the angle of inclination of thepillar-shaped objects is made constant, incident light is more stablyreflected within the bent columnar structure, and therefore, theincident angle dependency originating from the bent columnar structurecan be further enhanced.

More specifically, as illustrated in FIG. 1(b), it is preferable thatthe angle of inclination θa, with respect to the normal line of the filmplane, of the pillar-shaped objects 12 a as a highly refractive region12 in the portion upper than the bent section 14 in the bent columnarstructure 20 a as the first internal structure 20, is adjusted to avalue within the range of 0° to 30°.

The reason for this is that when the angle of inclination θa has a valueof above 30°, the absolute value of the incident angle of active energyradiation also becomes large accordingly, thereby the proportion ofreflection of the active energy radiation at the interface between airand the coating layer increases, and on the occasion of forming the bentcolumnar structure, it becomes necessary to irradiate the opticaldiffusion film with active energy radiation with higher illuminance. Onthe other hand, in a case in which the active energy radiation indeedenters at 0°, there is a possibility that a factor causing bending maynot be obtained, and consequently, there is a possibility that bendingmay not occur.

Therefore, it is more preferable that the angle of inclination θa isadjusted to a value of 0.5° or more, and even more preferably to a valueof 1° or more.

It is also more preferable that the angle of inclination θa is adjustedto a value of 25° or less, and even more preferably to a value of 20° orless.

Furthermore, as illustrated in FIG. 1(b), it is preferable that theangle of inclination θb, with respect to the normal line of the filmplane, of the pillar-shaped objects 12 a in the lower portion of thebent section 14 in the bent columnar structure 20 a as the firstinternal structure 20 is adjusted to a value within the range of 1° to60°.

The reason for this is that when the angle of inclination θb has a valueof below 1°, even if a synergistic effect with the pillar-shaped objectsin the portion upper than the bent section is considered, it may bedifficult to sufficiently obtain an effect of expanding the opticaldiffusion incident angle region. On the other hand, when the angle ofinclination θb has a value of above 60°, since the absolute value of theincident angle of active energy radiation also becomes larger, theproportion of reflection of active energy radiation at the interfacebetween air and the coating layer increases, and on the occasion offorming a bent columnar structure, there is a need to irradiate theoptical diffusion film with active energy radiation with higherilluminance. Furthermore, when a synergistic effect with thepillar-shaped objects in the portion upper than the bent section isconsidered, the optical diffusion incident angle region can besufficiently expanded even without further increasing the angle ofinclination.

Therefore, it is more preferable that the angle of inclination θb isadjusted to a value of 3° or more, and even more preferably to a valueof 5° or more.

It is also more preferable that the angle of inclination θb is adjustedto a value of 55° or less, and even more preferably to a value of 50° orless.

Furthermore, it is preferable that the absolute value of θb−θa isadjusted to a value of 1° or more, more preferably to a value of 3° ormore, and even more preferably to a value of 5° or more.

It is also preferable that the absolute value of θb−θa is adjusted to avalue of 30° or less, more preferably to a value of 25° or less, andeven more preferably to a value of 20° or less.

Meanwhile, θa and θb mean the angles of inclination (°) of pillar-shapedobjects obtainable in a case in which the angle of the normal line withrespect to the film surface, which is measured at a cross-section whenthe film is cut along a plane that is perpendicular to the film planeand cuts the entirety of one pillar-shaped object into two along theaxial line, is designated as 0°.

More specifically, as illustrated in FIG. 1(b), θa means the angle of anarrower side between the angles formed by the normal line of the filmplane and the axial line at the top of the pillar-shaped objects in theportion upper than the bent section.

Furthermore, θb means the angle on the narrower side between the anglesformed by the normal line of the film plane and the axial line at thetop of the pillar-shaped objects in the portion lower than the bentsection.

(2) Bent Louver Structure

As illustrated in FIGS. 4(a) and 4(b), it is preferable that the firstinternal structure is a bent louver structure 20 b in which a pluralityof plate-shaped regions (11, 12 b) having different refractive indicesare alternately disposed in any one direction along the film plane, andthat the first internal structure is a bent louver structure 20 b inwhich the plate-shaped regions (11, 12 b) have a bent section 14 at anintermediate point along the film thickness direction.

The reason for this is that when such a bent louver structure is used, adistinct first internal structure having a predetermined difference inrefractive index can be formed, and also, a distinct bent section can beprovided in the regions having a relatively high refractive index.

(2)-1 Refractive Index

It is preferable that the relation between the refractive index of theplate-shaped regions having a relatively high refractive index and therefractive index of the plate-shaped regions having a relatively lowrefractive index in the bent louver structure is regulated to be thesame as the relation between the refractive index of the pillar-shapedobjects having a relatively high refractive index and the refractiveindex of the pillar-shaped objects having a relatively low refractiveindex in the bent columnar structure as described above.

(2)-2 Width

Furthermore, it is preferable that the width of the high refractiveindex plate-shaped regions 12 b and the low refractive indexplate-shaped regions 11 having different refractive indices in the bentlouver structure 20 b illustrated in FIGS. 4(a) and 4(b), is adjusted tobe the same as the maximum diameter in a cross-section of thepillar-shaped objects and the interval between the pillar-shaped objectsin the bent columnar structure as described above.

(2)-3 Thickness

It is preferable that the thickness of the bent louver structure 20 b(length in the film thickness direction) illustrated in FIGS. 4(a) and4(b) is adjusted to be the same as the thickness of the bent columnarstructure as described above.

(2)-4 Angle of Inclination

It is also preferable that the angle of inclination of the plate-shapedregions (11, 12 b) having different refractive indices in the bentlouver structure 20 b illustrated in FIGS. 4(a) and 4(b) is adjusted tobe the same as the angle of inclination of the pillar-shaped objects inthe bent columnar structure as described above.

The angle of inclination of the plate-shaped regions means the angle ofinclination (°) of plate-shaped regions in a case in which the angle ofthe normal line with respect to the film surface, which is measured at across-section when the film is cut at a plane perpendicular to theplate-shaped region extending in any one direction along the film plane,is designated as 0°.

4. Second Internal Structure

The second internal structure in the optical diffusion film of theinvention has basically the same configuration as that of the firstinternal structure as described above, and therefore, repeateddescription of specific matters will not be given here.

However, it is preferable that unlike the first internal structure asdescribed above, as illustrated in FIG. 1(a) and FIGS. 4(a) and 4(b),the regions having a relatively high refractive index do not have a bentsection at an intermediate point along the film thickness direction.

The reason for this is speculated that the second internal structure isformed by irradiating the optical diffusion film with active energyradiation at low illuminance, and since the upper limit of the thicknessis limited, it is difficult to form a bent internal structure having asufficient length in the vertical direction.

Furthermore, the composition of the region where an internal structureis not formed, in which the second internal structure is to be formed,is different from the composition of the initial composition for anoptical diffusion film because the first internal structure has alreadybeen formed, and therefore, the composition tends to be separated in thevertical direction in the second internal structure.

Accordingly, it is speculated that in the second internal structure,there is a tendency that bending is not easily formed due to suchseparation of composition.

Furthermore, it is also speculated to be because the ultravioletabsorber is consumed up for the first internal structure because thefirst internal structure is formed first, and there is no ultravioletabsorber remaining in the region where an internal structure is notformed, which is needed for bending the second internal structure.

It is preferable that the thickness (length in the film thicknessdirection) of the second internal structure (30 a, 30 b) as illustratedin FIG. 1(a) and FIGS. 4(a) and 4(b), that is, L2 in FIG. 1(b), isadjusted to a value within the range of 10 to 200 μm.

The reason for this is that the second internal structure is a part thataccomplishes an ancillary role in optical diffusion with respect to thefirst internal structure.

Therefore, it is more preferable that the length L2 of the secondinternal structure is adjusted to a value of 20 μm or more, and evenmore preferably to a value of 40 μm or more.

It is also more preferable that the length L2 of the second internalstructure is adjusted to a value of 150 μm or less, and even morepreferably to a value of 100 μm or less.

For the same reason as the case of the angle of inclination θa, it ispreferable that the angle of inclination θc of the regions 12′ having arelatively high refractive index in the second internal structure 30 asillustrated in FIG. 1(b) is adjusted to a value within the range of 0°to 30°.

Therefore, it is more preferable that the angle of inclination θc isadjusted to a value of 25° or less, and even more preferably to a valueof 20° or less.

Furthermore, it is preferable that the angles of inclination θa, θb andθc are inclined to the same side (also including the angle ofinclination of 0°), while the angles of inclination become graduallylarger in this sequence.

The reason for this is that as the angles of inclination graduallychange, the optical diffusion incident angle regions originating fromthe respective internal structures also overlap, and the changes in theoptical diffusion characteristics associated with variation in theincident angle of incident light can be more effectively suppressed.

5. Overlapping Internal Structure

As illustrated in FIG. 1(b), it is preferable that the optical diffusionfilm 10 of the invention has an overlapping internal structure 40 inwhich the position of the upper end of the first internal structure 20and the position of the lower end of the second internal structure 30overlap with each other in the film thickness direction.

The reason for this is that when the optical diffusion film has anoverlapping internal structure, the generation of scattered light can beeffectively suppressed, and the uniformity of the intensity of diffusedlight can be enhanced, compared to a case in which the portion in whichan internal structure is not formed exists between the respectiveinternal structures.

In the following description, the overlapping internal structure will bespecifically explained.

(1) Embodiment

The overlapping internal structure is not particularly limited as longas the position of the upper end of the first internal structure and theposition of the lower end of the second internal structure are formed soas to overlap with each other in the film thickness direction.

More specifically, it is preferable that, as illustrated in FIG. 5(a),the overlapping internal structure is an overlapping columnar structure40 in which the tips of the regions having a relatively high refractiveindex (12, 12′), which originate from any one of the first internalstructure 20 and the second internal structure 30, are in contact withthe vicinity of the tips of the regions having a relatively highrefractive index (12′, 12), which originate from the other internalstructure (30, 20).

Alternatively, it is also preferable that, as illustrated in FIG. 5(b),the overlapping internal structure is an overlapping internal structure40 in which the regions having a relatively high refractive index (12,12′), which originate from any one of the first internal structure 20and the second internal structure 30, overlap with such regions of thesame kind in a non-contact state.

(2) Difference in Angle of Inclination

It is preferable that the absolute value of the difference between theangles of inclination (θa, θc) of the regions having relatively highrefractive indices (12, 12′), which respectively originate from thefirst internal structure 20 and the second internal structure 30, isadjusted to a value of 1° or more.

The reason for this is that when the absolute value of the differencebetween the angles of inclination is adjusted to a value of 1° or more,the optical diffusion incident angle regions can be more effectivelyexpanded. On the other hand, if the absolute value of the differencebetween the angles of inclination has an excessively large value, theoptical diffusion incident angle regions attributable to the variousinternal structures of the optical diffusion film become perfectlyindependent of each other, and the overall optical diffusion incidentangle regions of the film may not be efficiently expanded.

Therefore, it is more preferable that the absolute value of thedifference between the angles of inclination is adjusted to a value of2° or more, and even more preferably to a value of 5° or more.

Furthermore, it is also preferable that the absolute value of thedifference between the angles of inclination is adjusted to a value of30° or less, and even more preferably to a value of 20° or less.

(3) Thickness

It is preferable that the thickness (length in the film thicknessdirection) L3 of the overlapping internal structure illustrated in FIG.1(b) is adjusted to a value within the range of 1 to 40 μm.

The reason for this is that if the length L3 has a value of below 1 μm,scattered light is likely to be generated at the connection part of therespective internal structures, and it may be difficult to retain theuniformity of the intensity of diffused light more stably. On the otherhand, it is because if the length L3 has a value of above 40 μm, theefficiency for extracting diffused light may be decreased. That is, in acase in which the length of the overlapping internal structure is toolong, it is expected that backscattering or the like may occur in therelevant region, and a decrease in the efficiency for extractingdiffused light may be brought about.

Therefore, it is more preferable that the length L3 of the overlappinginternal structure is adjusted to a value of 3 μm or more, and even morepreferably to a value of 5 μm or more.

It is also more preferable that the length L3 of the overlappinginternal structure is adjusted to a value of 35 μm or less, and evenmore preferably to a value of 30 μm or less.

6. Total Film Thickness

Furthermore, it is preferable that the total film thickness of theoptical diffusion film of the invention is adjusted to a value withinthe range of 60 to 700 μm.

The reason for this is that if the total film thickness of the opticaldiffusion film has a value of below 60 μm, the amount of incident lightthat propagates straight through the internal structure increases, andit may be difficult for the optical diffusion film to exhibit opticaldiffusion. On the other hand, it is because if the total film thicknessof the optical diffusion film has a value of above 700 μm, when aninternal structure is formed by irradiating a composition for an opticaldiffusion film with active energy radiation, the direction of progressof photopolymerization is diffused by the internal structure that hasbeen initially formed, and it may be difficult to form a desiredinternal structure.

Therefore, it is more preferable that the total film thickness of theoptical diffusion film is adjusted to a value of 80 μm or more, and evenmore preferably to a value of 100 μm or more.

Furthermore, it is more preferable that the total film thickness of theoptical diffusion film is adjusted to a value of 450 μm or less, andeven more preferably to a value of 250 μm or less.

7. Pressure-Sensitive Adhesive Layer

The optical diffusion film of the invention may also include apressure-sensitive adhesive layer for lamination of the opticaldiffusion film with other materials on one surface or on both surfacesof the optical diffusion film.

The pressure-sensitive adhesive that constitutes such apressure-sensitive adhesive layer is not particularly limited, and anyconventionally known acrylic, silicone-based, urethane-based, orrubber-based pressure-sensitive adhesive can be used.

Second Embodiment

A second embodiment of the invention relates to a method formanufacturing the optical diffusion film of the first embodiment, themethod being a method for manufacturing an optical diffusion filmincluding the following steps (a) to (d):

(a) a step of preparing a composition for an optical diffusion filmincluding at least two polymerizable compounds having differentrefractive indices, a photopolymerization initiator and an ultravioletabsorber, in which the content of the ultraviolet absorber has a valueof below 2 parts by weight (provided that 0 parts by weight is excluded)relative to the total amount (100 parts by weight) of the at least twopolymerizable compounds having different refractive indices;

(b) a step of applying the composition for an optical diffusion film ona process sheet, and forming a coating layer;

(c) a step of irradiating the coating layer with first active energyradiation, forming a first internal structure in the lower portion ofthe coating layer, and also leaving a region where an internal structureis not formed, in the upper portion of the coating layer; and

(d) a step of irradiating the coating layer with second active energyradiation, and forming a second internal structure in the region wherean internal structure is not formed.

In the following description, the second embodiment of the inventionwill be specifically explained with reference to the drawings, mainlybased on the differences between the second embodiment and the firstembodiment.

1. Step (a): Step of Preparing Composition for Optical Diffusion Film

Step (a) is a step of preparing a predetermined composition for anoptical diffusion film.

More specifically, it is preferable that two polymerizable compoundshaving different refractive indices and the like are stirred under hightemperature conditions of 40° C. to 80° C., and thereby a uniform mixedliquid is obtained.

Furthermore, it is preferable that a solution of the composition for anoptical diffusion film is obtained by further adding a diluent solventas necessary, in order to obtain a desired viscosity.

Step (a) will be more specifically explained in the followingdescription.

(1)(A) High Refractive Index Polymerizable Compound

(1)-1 Refractive Index

It is preferable that the refractive index of the polymerizable compoundhaving a higher refractive index (hereinafter, may be referred to ascomponent (A)) between the two polymerizable compounds having differentrefractive indices is adjusted to a value within the range of 1.5 to1.65.

The reason for this is that if the refractive index of the component (A)has a value of below 1.5, the difference between this value and therefractive index of the polymerizable compound having a lower refractiveindex (hereinafter, may be referred to as component (B)) becomes toosmall, and it may be difficult to obtain an effective optical diffusionangle region. On the other hand, it is because if the refractive indexof the component (A) has a value of above 1.65, the difference betweenthis value and the refractive index of the component (B) becomes larger;however, it may be difficult to form even an apparently compatible statewith the component (B).

Therefore, it is more preferable that the refractive index of thecomponent (A) is adjusted to a value of 1.55 or more, and even morepreferably to a value of 1.56 or more.

It is also more preferable that the refractive index of the component(A) is adjusted to a value of 1.6 or less, and even more preferably to avalue of 1.59 or less.

The refractive index of the component (A) as described above means therefractive index of the component (A) before the component is cured bylight irradiation.

Furthermore, the refractive index can be measured according to, forexample, JIS K0062.

Meanwhile, the term “optical diffusion angle region” means the range ofthe diffusion angle of diffused light obtainable in a state in which apoint light source is fixed at an angle at which incident light is mostdiffused in an optical diffusion film.

The width” of the “optical diffusion angle region” is known to be almostequal to the width of the “optical diffusion incident angle region”.

(1)-2 Type

The type of component (A) is not particularly limited; however, examplesthereof include biphenyl (meth)acrylate, naphthyl (meth)acrylate,anthracyl (meth)acrylate, benzylphenyl (meth)acrylate, biphenyloxyalkyl(meth)acrylate, naphthyloxyalkyl (meth)acrylate, anthracyloxyalkyl(meth)acrylate, benzylphenyloxyalkyl (meth)acrylate, and compoundsobtainable by partially substituting the aforementioned compounds with ahalogen, an alkyl, an alkoxy, an alkyl halide or the like.

The term “(meth)acrylic acid” means both acrylic acid and methacrylicacid.

Also, it is more preferable that a compound containing a biphenyl ringis included as the component (A), and particularly, it is even morepreferable that a biphenyl compound represented by the following Formula(1) is included.

wherein in Formula (1), R¹ to R¹⁰ are respectively independent of eachother, and at least one of R¹ to R¹⁰ represents a substituentrepresented by the following Formula (2), while the others eachrepresent any one substituent selected from a hydrogen atom, a hydroxylgroup, a carboxyl group, an alkyl group, an alkoxy group, an alkylhalide group, a hydroxyalkyl group, a carboxyalkyl group, and a halogenatom.

wherein in Formula (2), R¹¹ represents a hydrogen atom or a methylgroup; the number of carbon atoms n represents an integer from 1 to 4;and the number of repetitions m represents an integer from 1 to 10.

The reason for this is speculated that when a biphenyl compound having aparticular structure is included as the component (A), a predetermineddifference is made between the rates of polymerization of the component(A) and the component (B), compatibility between the component (A) andthe component (B) is lowered to a predetermined range, andcopolymerizability between the two components can be deteriorated.

Furthermore, the difference between the refractive index of the highrefractive index region originating from the component (A) and therefractive index of the low refractive index region originating from thecomponent (B) can be more easily regulated to a value larger than orequal to a predetermined value, by increasing the refractive index ofthe high refractive index region originating from the component (A).

(1)-3 Content

Furthermore, it is preferable that the content of the component (A) inthe composition for an optical diffusion film is adjusted to a valuewithin the range of 25 to 400 parts by weight relative to 100 parts byweight of the component (B) that will be described below.

The reason for this is that if the content of the component (A) has avalue of below 25 parts by weight, the existence ratio of the component(A) with respect to the component (B) becomes small, the width of thehigh refractive index region originating from the component (A) becomesexcessively small compared to the width of the low refractive indexregion originating from the component (B), and it may be difficult toobtain a predetermined internal structure having satisfactory incidentangle dependency. On the other hand, it is because if the content of thecomponent (A) has a value of above 400 parts by weight, the existenceratio of the component (A) with respect to the component (B) becomeslarge, the width of the high refractive index region originating fromthe component (A) becomes excessively large compared to the width of thelow refractive index region originating from the component (B), and incontrast, it may be difficult to obtain a predetermined internalstructure having satisfactory incident angle dependency.

Therefore, it is more preferable that the content of the component (A)is adjusted to a value of 40 parts by weight or more, and even morepreferably to a value of 50 parts by weight or more, relative to 100parts by weight of the component (B).

Furthermore, it is more preferable that the content of the component (A)Is adjusted to a value of 300 parts by weight or less, and even morepreferably to a value of 200 parts by weight or less, relative to 100parts by weight of the component (B).

(2) Low Refractive Index Polymerizable Compound

(2)-1 Refractive Index

It is preferable that the refractive index of component (B), that is,the polymerizable compound having a lower refractive index between thetwo polymerizable compounds having different refractive indices, isadjusted to a value within the range of 1.4 to 1.5.

The reason for this is that if the refractive index of the component (B)has a value of below 1.4, the difference between the refractive index ofthe component (B) and the refractive index of the component (A) becomeslarge; however, compatibility with the component (A) is extremelydeteriorated, and it may be difficult to form a predetermined internalstructure. On the other hand, it is because if the refractive index ofthe component (B) has a value of above 1.5, the difference between therefractive index of the component (B) and the refractive index of thecomponent (A) becomes too small, and it may be difficult to obtaindesired incident angle dependency.

Therefore, it is more preferable that the refractive index of thecomponent (B) is adjusted to a value of 1.45 or more, and even morepreferably to a value of 1.46 or more.

It is also more preferable that the refractive index of the component(B) is adjusted to a value of 1.49 or less, and even more preferably toa value of 1.48 or less.

The refractive index of the component (B) described above means therefractive index of the component (B) before being cured by lightirradiation.

Furthermore, the refractive index can be measured according to, forexample, JIS K0062.

Furthermore, it is preferable that the difference between the refractiveindex of the component (A) and the refractive index of the component (B)as described above is adjusted to a value of 0.01 or more.

The reason for this is that if such difference in the refractive indexhas a value of below 0.01, the range of the angle at which incidentlight is fully reflected within a predetermined internal structure isnarrowed, and therefore, the optical diffusion angle region may becomeexcessively narrow. On the other hand, it is because the difference inthe refractive index as an excessively large value, compatibilitybetween the component (A) and the component (B) is excessivelydeteriorated, and it may be difficult to form a predetermined internalstructure.

Therefore, it is more preferable that the difference between therefractive index of the component (A) and the refractive index of thecomponent (B) is adjusted to a value of 0.05 or more, and even morepreferably to a value of 0.1 or more.

It is also more preferable that the difference between the refractiveindex of the component (A) and the refractive index of the component (B)is adjusted to a value of 0.5 or less, and even more preferably to avalue of 0.2 or less.

The refractive indices of the component (A) and the component (B) asused herein mean the refractive indices of the component (A) and thecomponent (B) before being cured by light irradiation.

(2)-2 Type

Furthermore, the type of the component (B) is not particularly limited;however, examples thereof include urethane (meth)acrylate, a(meth)acrylic polymer having a (meth)acryloyl group in a side chain, a(meth)acryloyl group-containing silicone resin, and an unsaturatedpolyester resin. However, it is particularly preferable to use urethane(meth)acrylate.

The reason for this is that when urethane (meth)acrylate is used, thedifference between the refractive index of the high refractive indexregion originating from the component (A) and the refractive index ofthe low refractive index region originating from the component (B) canbe more easily regulated, the variation in the refractive index of thelow refractive index region originating from the component (B) iseffectively suppressed, and the optical diffusion film including apredetermined internal structure can be more efficiently obtained.

Meanwhile, (meth)acrylate means both acrylate and methacrylate.

(3) Photopolymerization Initiator

Furthermore, in regard to the composition for an optical diffusion filmaccording to the second embodiment of the invention, it is preferablethat a photopolymerization initiator is incorporated as component (C),if desired.

The reason for this is that by incorporating a photopolymerizationinitiator, a predetermined internal structure can be efficiently formedwhen the composition for an optical diffusion film is irradiated withactive energy radiation.

Here, the photopolymerization initiator refers to a compound whichgenerates a radical species through irradiation with active energyradiation such as ultraviolet radiation.

Examples of such a photopolymerization initiator include benzoin,benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether,benzoin n-butyl ether, benzoin isobutyl ether, acetophenone,dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone,2,2-diethoxy-2-phenylacetophenone,2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroycyclohexyl phenylketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one,4-(2-hydroxyethoxy)phenyl-2-(hydroxy-2-propyl) ketone, benzophenone,p-phenylbenzophenone, 4,4-diethylaminobenzophenone,dichlorobenzophenone, 2-methylanthraquinone, 2-ethylanthraquinone,2-tertiary-butylanthraquinone, 2-aminoanthraquinone,2-methylthioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone,2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, benzyl dimethylketal, acetophenone dimethyl ketal, acetophenone dimethyl ketal,p-dimethylamine benzoic acid ester, andoligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propane]. These maybe used singly, or two or more kinds thereof may be used in combination.

In a case in which a photopolymerization initiator is used, the contentthereof is preferably adjusted to a value within the range of 0.2 to 20parts by weight, more preferably to a value within the range of 0.5 to15 parts by weight, and even more preferably to a value within the rangeof 1 to 10 parts by weight relative to the total amount of 100 parts byweight of the component (A) and the component (B).

(4) Ultraviolet Absorber

(4)-1 Type

It is preferable that the composition for an optical diffusion filmaccording to the second embodiment of the invention includes anultraviolet absorber as component (D).

The reason for this is that by incorporating an ultraviolet absorber ascomponent (D), when the composition is irradiated with active energyradiation, the composition for an optical diffusion film can selectivelyabsorb active energy radiation having a predetermined wavelength in apredetermined range.

As a result, bending can be induced in the first internal structureformed within the film, without inhibiting curing of the composition foran optical diffusion film.

Here, at this moment, a specific mechanism by which an ultravioletabsorber causes bending in the first internal structure that is formedin the film has not been sufficiently elucidated.

However, the mechanism is speculated as follows.

A tendency has been confirmed, in which as the amount of addition of theultraviolet absorber is smaller, the angle of bending becomes smaller,and the optical diffusion angle region is narrowed.

Furthermore, it has been confirmed that as the ultraviolet absorber hasa peak at a wavelength closer to the wavelength of 365 nm, which is themain wavelength of a high pressure mercury lamp, bending is induced witha smaller amount of addition of the ultraviolet absorber.

Therefore, it is speculated that as the wavelength of ultravioletemitted from a high pressure mercury lamp is controlled by theultraviolet absorber, that is, as the intensity ratios of variouswavelengths in the ultraviolet radiation emitted from the high pressuremercury lamp varies, the progress of polymerization toward the lowerpart in the film thickness direction in the coating layer is delayed,and the direction of progress of polymerization is changed at a depth atwhich polymerization has progressed to a certain extent.

Regarding a factor that causes a change in the direction of progress ofpolymerization, the difference between the refractive indices of thecomponent (A) and the component (B) may be considered; however, based oncalculations, such difference in the refractive index does not causebending to an extent that can be actually recognized.

Furthermore, it is preferable that the component (D) is at least oneselected from the group consisting of a hydroxyphenyltriazine-basedultraviolet absorber, a benzotriazole-based ultraviolet absorber, abenzophenone-based ultraviolet absorber, and a hydroxybenzoate-basedultraviolet absorber.

The reason for this is that when these ultraviolet absorbers are used,bending can be induced more reliably in the first internal structure,and therefore, the optical diffusion incident angle region in theresulting optical diffusion film can be more effectively expanded.

That is, it is because it has been confirmed that when these ultravioletabsorbers having peaks at wavelengths that are closer to the wavelengthof 365 nm, which is the main wavelength of a high pressure mercury lamp,are used, bending is induced with small amounts of addition of theultraviolet absorbers.

(4)-2 Absorption Wavelength

It is also preferable that the component (D) has an absorption peak forlight having a wavelength of 330 to 380 nm.

The reason for this is that when the absorption peak of the component(D) is within the range described above, the composition for an opticaldiffusion film can efficiently absorb energy at 365 nm, which is themain wavelength of a high pressure mercury lamp, and a first internalstructure having a bending can be efficiently formed in the resultingoptical diffusion film.

Meanwhile, regarding ultraviolet absorbers having absorption peaks atwavelengths of below 330 nm, many of them exhibit very low absorption oflight having a wavelength of 365 nm. Therefore, even if such anultraviolet absorber is used, a first internal structure havingsufficient bending may not be formed in the resulting optical diffusionfilm.

On the other hand, regarding ultraviolet absorbers having absorptionpeaks at wavelengths of above 380 nm, many of them definitely exhibitabsorption of light having a wavelength of 365 nm. However, suchultraviolet absorbers often have absorption over the entire ultravioletregion, and in order to gain absorption at 365 nm, it is necessary toincrease the amount of addition of the ultraviolet absorber. As aresult, in a case in which an ultraviolet absorber having an absorptionpeak at a wavelength of above 380 nm is used, curing of the opticaldiffusion film may be inhibited per se.

Therefore, it is more preferable that the component (d) is regulated tohave an absorption peak at a wavelength in the range of 335 to 375 nm,and even more preferably at a wavelength in the range of 340 to 370 nm.

(4)-3 Content

It is preferable that the content of the component (D) in thecomposition for an optical diffusion film is adjusted to value of below2 parts by weight (provided that 0 parts by weight is excluded) relativeto the total amount (100 parts by weight) of the component (A) and thecomponent (B).

The reason for this is that when the content of the component (D) isadjusted to a value within such a range, bending can be induced in thefirst internal structure formed within the film, without inhibitingcuring of the composition for an optical diffusion film, and thereby,the optical diffusion incident angle region can be effectively expandedin the resulting optical diffusion film.

That is, it is because if the content of the component (D) has a valueof 2 parts by weight or more, curing of the composition for an opticaldiffusion film is inhibited, shrinkage wrinkles may occur at the filmsurface, or curing may not proceed at all. On the other hand, it isbecause if the content of the component (D) becomes excessively small,it may be difficult to induce sufficient bending in the first internalstructure that is formed within the film, and it may be difficult toeffectively expand the optical diffusion incident angle region in theresulting optical diffusion film.

Therefore, it is more preferable that the content of the component (D)is adjusted to a value of 0.01 parts by weight or more, and even morepreferably to a value of 0.02 parts by weight or more, relative to thetotal amount (100 parts by weight) of the component (A) and thecomponent (B).

Furthermore, it is more preferable that the content of the component (D)is adjusted to a value of 1.5 parts by weight or less, and even morepreferably to a value of 1 part by weight or less, relative to the totalamount (100 parts by weight) of the component (A) and the component (B).

(5) Other Additives

Other additives can also be added as appropriate, to the extent that theeffects of the invention are not impaired.

Examples of the other additives include an oxidation inhibitor, anantistatic agent, a polymerization accelerator, a polymerizationinhibitor, an infrared absorber, a plasticizer, a diluent solvent, and aleveling agent.

Meanwhile, generally, the content of the other additives is preferablyadjusted to a value within the range of 0.01 to 5 parts by weightrelative to the total amount (100 parts by weight) of the component (A)and the component (B).

2. Step (b): Application Step

Step (b) is a step of applying the composition for an optical diffusionfilm thus prepared on a process sheet 2, and forming a coating layer 1,as illustrated in FIG. 6(a).

Regarding the process sheet, a plastic film and paper can both be used.

Above all, examples of the plastic film include a polyester-based filmsuch as a polyethylene terephthalate film; a polyolefin-based film suchas a polyethylene film or a polypropylene film; a cellulose-based filmsuch as a triacetyl cellulose film; and a polyimide-based film.

Examples of the paper include glassine paper, coated paper, andlaminated paper.

When the steps that will be described below are considered, the processsheet 2 is preferably a film having excellent dimensional stabilityagainst heat or active energy radiation.

Regarding such a film, among those mentioned above, a polyester-basedfilm, a polyolefin-based film, and a polyimide-based film may bepreferably used.

Furthermore, in regard to the process sheet, in order to allow easydetachment of the optical diffusion film thus obtained from the processsheet after photocuring, it is preferable to provide a release layer onthe surface that has been coated with the composition for an opticaldiffusion film in the process sheet.

Such a release layer can be formed using a conventionally known releaseagent such as a silicone-based release agent, a fluorine-based releaseagent, an alkyd-based release agent, or an olefin-based release agent.

Usually, the thickness of the process sheet is preferably adjusted to avalue within the range of 25 to 200 μm.

Regarding the method of applying a composition for an optical diffusionfilm on a process sheet, for example, application can be performed by aconventionally known method such as a knife coating method, a rollcoating method, a bar coating method, a blade coating method, a diecoating method, or a gravure coating method.

At this time, the thickness of the coating layer is preferably adjustedto a value within the range of 10 to 700 μm.

3. Step (c): First Active Energy Ray Irradiation Step

Step (c) is a step of subjecting the coating layer 1 to firstirradiation with active energy radiation, thus forming a first internalstructure 20 in the lower portion of the coating layer 1, and alsoleaving a region 20′ where an internal structure is not formed, in theupper portion of the coating layer 1, as illustrated in FIGS. 6(b) and6(c).

In the following description, the first active energy ray irradiationstep will be explained, separately for the case of forming a bentcolumnar structure and the case of forming a bent louver structure.

(1) In Case of Forming Bent Columnar Structure

In a case in which a bent columnar structure is formed as a firstinternal structure, as illustrated in FIG. 6(b), the coating layer 1formed on the process sheet is irradiated with parallel light 60 havinga high degree of parallelism of light rays as the light for irradiation.

Here, the term parallel light means light in which the direction ofemitted light is substantially parallel without any expansion even ifviewed from any direction.

Specifically, it is preferable that the degree of parallelism of thelight for irradiation is set to a value of 10° or less.

The reason for this is that when the degree of parallelism of the lightfor irradiation is set to a value within such a range, a bent columnarstructure in which a plurality of pillar-shaped objects are arranged soas to stand closes together at a certain angle of inclination in thefilm thickness direction, can be formed efficiently and stably.

Therefore, it is more preferable that the degree of parallelism of thelight for irradiation is adjusted to a value of 5° or less, and evenmore preferably to a value of 2° or less.

Regarding the angle of irradiation of the light for irradiation, asillustrated in FIG. 7, it is preferable that the angle of irradiation θ1obtainable in a case in which the angle of the normal line with respectto the surface of the coating layer 1 is designated as 0°, is adjustedto a value within the range of, usually, −80° to 80°.

The reason for this is that if the angle of irradiation has a value thatis not in the range of −80° to 80°, the influence of reflection or thelike at the surface of the coating layer 1 may become significant, andit may be difficult to form a satisfactory bent columnar structure.

Meanwhile, arrow B in FIG. 7 represents the direction of movement of thecoating layer.

Regarding the light for irradiation, it is preferable to use ultravioletradiation.

The reason for this is that in the case of an electron beam, since therate of polymerization is very fast, the component (A) and the component(B) may not be able to sufficiently undergo phase separation during thecourse of polymerization, and it may be difficult to form a bentcolumnar structure. On the other hand, it is because when compared tovisible light or the like, ultraviolet radiation is associated with arich variety of ultraviolet-curable resins that are cured whenirradiated with ultraviolet radiation, or a rich variety ofphotopolymerization initiators that can be used, and therefore, theranges of selection for the component (A) and the component (B) can befurther widened.

Furthermore, regarding the conditions for the first irradiation withactive energy radiation, it is preferable that the peak illuminance atthe coating layer surface is adjusted to a value within the range of 0.1to 3 mW/cm².

The reason for this is that if such peak illuminance has a value ofbelow 0.1 mW/cm², a sufficient region where an internal structure is notformed can be secured; however, it may be difficult to form a distinctbent columnar structure. On the other hand, it is because if the peakilluminance has a value of above 3 mW/cm², even if there exists a regionwhere an internal structure is not formed, it is speculated that thecuring reaction in the relevant region may excessively proceed, andthus, it may be difficult to satisfactorily form a second internalstructure during the second active energy ray irradiation step that willbe described below.

Therefore, it is more preferable that the peak illuminance at thecoating layer surface during the first irradiation with active energyradiation is adjusted to a value of 0.3 mW/cm² or more, and even morepreferably to a value of 0.5 mW/cm² or more.

It is also more preferable that the peak illuminance at the coatinglayer surface during the first irradiation with active energy radiationis adjusted to a value of 2 mW/cm² or less, and even more preferably toa value of 1.5 mW/cm² or less.

Furthermore, it is preferable that the cumulative amount of light at thecoating layer surface during the first irradiation with active energyradiation is adjusted to a value within the range of 5 to 100 mJ/cm².

The reason for this is that if the cumulative amount of light has avalue of below 5 mJ/cm², it may be difficult to sufficiently extend thebent columnar structure from the upper side toward the lower part, orwhen the second internal structure is formed, the bent columnarstructure may be deformed. On the other hand, it is because if thecumulative amount of light has a value of above 100 mJ/cm², curing ofthe region where an internal structure is not formed may excessivelyproceed, and during the second active energy ray irradiation step thatwill be described below, it may be difficult to satisfactorily form thesecond internal structure.

Therefore, it is more preferable that the cumulative amount of light atthe coating layer surface during the first irradiation with activeenergy radiation is adjusted to a value of 7 mJ/cm² or more, and evenmore preferably to a value of 10 mJ/cm² or more.

It is also more preferable that the cumulative amount of light at thecoating layer surface during the first irradiation with active energyradiation is adjusted to a value of 50 mJ/cm² or less, and even morepreferably to a value of 30 mJ/cm² or less.

Furthermore, from the viewpoint of stably forming a bent columnarstructure while maintaining mass productivity, it is preferable thatwhen the first irradiation with active energy radiation is performed,the coating layer formed on the process sheet is moved at a rate withinthe range of 0.1 to 10 m/min.

Particularly, it is more preferable that the coating layer is moved at arate of 0.2 m/min or more, and even more preferably at a rate of 3 m/minor less.

Furthermore, from the viewpoint of efficiently leaving the region wherean internal structure is not formed, the first active energy rayirradiation step is performed in an oxygen-containing atmosphere(preferably, in an air atmosphere).

The reason for this is that when the first irradiation with activeenergy radiation is performed in an oxygen-containing atmosphere, whilea bent columnar structure is efficiently formed in the lower portion ofthe coating layer, the region where a internal structure is not formedcan be stably caused to remain in the upper portion of the coating layerby utilizing the influence of oxygen inhibition.

That is, it is because if the first irradiation with active energyradiation is performed not in an oxygen-containing atmosphere, but in anon-oxygen atmosphere that does not contain oxygen, a bent columnarstructure may be formed continuously almost up to the edge surface ofthe film, without leaving the region where an internal structure is notformed in the upper part of the film.

Meanwhile, the phrase “in an oxygen-containing atmosphere” means theconditions in which the top face of the coating layer is in directcontact with a gas containing oxygen, such as air. Above all, the phrase“in an air atmosphere” means the conditions in which the top face of thecoating layer is in direct contact with air.

Therefore, performing the first irradiation with active energy radiationin a state in which the top face of the coating layer is directlyexposed to air without implementing particular means such as laminationof a film on the top face of the coating layer or purging of theatmosphere with nitrogen, corresponds to the first irradiation withactive energy radiation “in an air atmosphere”.

(2) In Case of Forming Bent Louver Structure

In a case in which a bent louver structure is formed as the firstinternal structure, as illustrated in FIG. 6(c), the coating layer 1formed on the process sheet is irradiated with light that issubstantially parallel light when viewed from one direction but appearsas non-parallel random light when viewed from another direction.

Such light can be radiated using, for example, a linear light source125, and in this case, the light appears as substantially parallel lightwhen viewed from the axial direction of the linear light source 125, butappears as non-parallel random light 70′ when viewed from anotherdirection.

Meanwhile, other conditions for irradiation are equivalent to theconditions applicable to “In case of forming bent columnar structure” asdescribed above, and therefore, further description thereon will not begiven here.

4. Step (d): Second Active Energy Ray Irradiation Step

Step (d) is a step of further subjecting the coating layer to secondirradiation with active energy radiation, and forming a second internalstructure in the region where an internal structure is not formed.

The second active energy ray irradiation step as such can be performedbasically in the same manner as in the first active energy rayirradiation step.

Therefore, in a case in which a columnar structure is formed as thesecond internal structure in the second active energy ray irradiationstep, as illustrated in FIG. 6(b), it is desirable to irradiate theoptical diffusion film with parallel light. In a case in which a louverstructure is formed as the second internal structure, as illustrated inFIG. 6(c), it is desirable to irradiate the optical diffusion film withlight that is substantially parallel light when viewed from onedirection but appears as non-parallel random light when viewed fromanother direction.

Furthermore, regarding the conditions for the second irradiation withactive energy radiation, it is preferable that the peak illuminance atthe coating layer surface is adjusted to a value within the range of 0.1to 20 mW/cm².

The reason for this is that if the peak illuminance has a value of below0.1 mW/cm², it may be difficult to form a distinct second internalstructure. On the other hand, it is because if such illuminance has avalue of above 20 mW/cm², it is speculated that the curing rate becomestoo fast, and the second internal structure may not be effectivelyformed.

Therefore, it is more preferable that the peak illuminance at thecoating layer surface during the second irradiation with active energyradiation is adjusted to a value of 0.3 mW/cm² or more, and even morepreferably to a value of 0.5 mW/cm² or more.

It is also more preferable that the peak illuminance at the coatinglayer surface during the second irradiation with active energy radiationis adjusted to a value of 10 mW/cm² or less, and even more preferably toa value of 5 mW/cm² or less.

Furthermore, it is preferable that the cumulative amount of light at thecoating layer surface during the second irradiation with active energyradiation is adjusted to a value within the range of 5 to 300 mJ/cm².

The reason for this is that if the cumulative amount of light has avalue of below 5 mJ/cm², it may be difficult to sufficiently extend thesecond internal structure from the upper side toward the lower part. Onthe other hand, it is because if the cumulative amount of light has avalue of above 300 mJ/cm², coloration may occur in the resulting film.

Therefore, it is more preferable that the cumulative amount of light atthe coating layer surface during the second irradiation with activeenergy radiation is adjusted to a value of 10 mJ/cm² or more, and evenmore preferably to a value of 20 mJ/cm² or more.

Furthermore, it is more preferable that the cumulative amount of lightat the coating layer surface during the second irradiation with activeenergy radiation is adjusted to a value of 200 mJ/cm² or less, and evenmore preferably to a value of 150 mJ/cm² or less.

It is also preferable that the second irradiation with active energyradiation is performed in a non-oxygen atmosphere.

The reason for this is that when the second irradiation with activeenergy radiation is performed in a non-oxygen atmosphere, the influenceof oxygen inhibition is suppressed in the region where an internalstructure is not formed, which is obtained by the first irradiation withactive energy radiation, and thereby a second internal structure can beformed efficiently.

That is, it is because if the second irradiation with active energyradiation is performed not in a non-oxygen atmosphere but in an oxygenatmosphere, when the optical diffusion film is irradiated at a highilluminance, the second internal structure could be formed at a veryshallow position in the vicinity of the surface; however, the differencein refractive index needed for optical diffusion may not be obtained.Furthermore, it is because when the optical diffusion film is irradiatedat a low illuminance, the second internal structure may not be formed inthe region where an internal structure is not formed, under theinfluence of oxygen inhibition.

The phrase “in a non-oxygen atmosphere” means the conditions in whichthe top face of the coating layer is not in direct contact with anoxygen atmosphere or an atmosphere containing oxygen.

Therefore, for example, performing the second irradiation with activeenergy radiation in a state in which a film is laminated on the top faceof the coating layer, or nitrogen purge is performed by replacing airwith nitrogen gas, corresponds to the second irradiation with activeenergy radiation in the “non-oxygen atmosphere”.

As discussed above, according to the present invention, since a firstinternal structure and a second internal structure are formed by firstirradiation with active energy radiation and second irradiation withactive energy radiation, respectively, the combination of the angles ofinclination of the regions having a relatively high refractive index inthe respective internal structures can be easily regulated.

That is, only by appropriately adjusting the angle of irradiation foreach of the active energy ray irradiation processes, the combination ofthe angles of inclination of the regions having a relatively highrefractive index in the respective internal structures can be easilyregulated.

EXAMPLES

Hereinafter, the invention will be described in more detail by way ofExamples.

Example 1

1. Synthesis of Component (B): Low Refractive Index PolymerizableCompound

One mol of a polypropylene glycol (PPG) having a weight averagemolecular weight of 9,200, 2 mol of isophorone diisocyanate (IPDI), and2 mol of 2-hydroxyethyl methacrylate (HEMA) were introduced into avessel, and the mixture was allowed to react according to a conventionalmethod. Thus, a polyether urethane methacrylate having a weight averagemolecular weight of 9,900 was obtained.

The weight average molecular weights of the polypropylene glycol and thepolyether urethane methacrylate are values measured by gel permeationchromatography (GPC) under the conditions described below, andcalculated relative to polystyrene standards.

-   -   GPC analyzer: manufactured by Tosoh Corp., HLC-8020    -   GPC column: manufactured by Tosoh Corp. (described below in the        order of passage)

TSK guard column HXL-H TSK gel GMHXL (x2) TSK gel G2000HXL

-   -   Analytic solvent: tetrahydrofuran    -   Analysis temperature: 40° C.

2. Production of Composition for Optical Diffusion Film

Next, 100 parts by weight of the polyether urethane methacrylate havinga weight average molecular weight of 9,900 thus obtained as component(B) was mixed with 150 parts by weight of o-phenylphenoxyethoxyethylacrylate represented by Formula (3) described above and having amolecular weight of 268 (manufactured by Shin Nakamura Chemical Co.,Ltd., NK ESTER A-LEN-10) as component (A), 20 parts by weight (8 partsby weight relative to the total amount (100 parts by weight) ofcomponent (A) and component (B)) of 2-hydroxy-2-methylpropiophenone ascomponent (C), and 0.5 parts by weight (0.2 parts by weight relative tothe total amount (100 parts by weight) of component (A) and component(B)) of a benzotriazole-based ultraviolet absorber (manufactured by BASFSE, TINUVIN 384-2) as component (D), and then heating and mixing wasperformed under the conditions of 80° C. Thus, a composition for anoptical diffusion film was obtained.

The refractive indices of the component (A) and the component (B) weremeasured according to JIS K0062 using an Abbe refractometer(manufactured by Atago Co., Ltd., Abbe refractometer DR-M2, Na lightsource, wavelength 589 nm), and the refractive indices were 1.58 and1.46, respectively.

3. Coating Process

Next, the composition for an optical diffusion film thus obtained wasapplied on a film-like transparent polyethylene terephthalate(hereinafter, referred to as PET) as a process sheet, and a coatinglayer having a film thickness of 198 μm was formed.

4. First Irradiation with Ultraviolet Radiation

Next, the coating layer was irradiated with parallel light having adegree of parallelism of 2° or less using an ultraviolet spot parallellight source (manufactured by Jatec Co., Ltd.), in which the degree ofparallelism of central light was controlled to be ±3° or less, such thatthe angle of irradiation θ1 as illustrated in FIG. 7 would be almost20°.

The peak illuminance employed at that time was 1.18 mW/cm², thecumulative amount of light was 24.1 mJ/cm², the lamp height was 240 mm,and the speed of movement of the coating layer was 0.2 m/min.

5. Second Irradiation with Ultraviolet Radiation

Next, after the first ultraviolet irradiation process was completed, arelease film having ultraviolet transmissibility (manufactured by LintecCorp., SP-PET382050) and having a thickness of 38 μm was laminated onthe exposed surface side of the coating layer, and the resultant wassubjected to a non-oxygen atmosphere.

Next, similarly to the first ultraviolet irradiation process, thecoating layer was irradiated with parallel light having a degree ofparallelism of 2° or less, over the release film from the same side asthat used in the first ultraviolet irradiation process, such that theangle of irradiation θ1 as illustrated in FIG. 7 would be almost 0°.Thus, an optical diffusion film having a film thickness of 198 μm wasobtained.

The peak illuminance at that time was 1.26 mW/cm², the cumulative amountof light was 22.4 mJ/cm², the lamp height was 240 mm, and the speed ofmovement of the coating layer was 0.2 m/min.

Meanwhile, the peak illuminance and the cumulative amount of lightdescribed above were measured by installing a UV meter (manufactured byEye Graphics Co., Ltd., EYE ultraviolet cumulative illuminometerUVPF-A1) equipped with a light collector at the position of the coatinglayer.

Furthermore, the film thickness of the optical diffusion film wasmeasured using a constant pressure thickness analyzer (manufactured byTakara Co., Ltd., TECLOCK PG-02J).

Furthermore, a schematic diagram of a cross-section obtained by cuttingthe optical diffusion film thus obtained, at a plane that is parallel tothe direction of movement of the coating layer and orthogonallyintersects the film plane, is shown in FIG. 8(a), and a photograph ofthe cross-section is shown in FIG. 8(b).

As illustrated in FIG. 8(a), the length L1 of the first columnarstructure was 142.2 μm, and in the first columnar structure as such, thelength La of the portion upper than the bent section was 41.0 μm, whilethe angle of inclination thereof θa was 15°.

Furthermore, in the first columnar structure, the length Lb of theportion lower than the bent section was 101.2 μm, and the angle ofinclination thereof θb was 32°.

The absolute value of θb−θa was 17°.

Furthermore, the length L2 of the second columnar structure was 71.8 μm,and the angle of inclination θc was 0°.

Moreover, there existed an overlapping columnar structure (overlappinginternal structure) in which the tips of pillar-shaped objectsoriginating from the second columnar structure were brought into contactwith the vicinity of the tips of pillar-shaped objects originating fromthe first columnar structure, and the length L3 of the overlappingcolumnar structure was 16 μm.

The absolute value of θa−θc in the overlapping internal structure was15°.

Cutting of the optical diffusion film was performed using a razor, andphotographing of a cross-section was performed by reflective observationusing a digital microscope (manufactured by Keyence Corp., VHX-2000).

In the schematic diagram of FIG. 8(a), high refractive index regions inthe internal structure are represented by solid lines (hereinafter, thesame).

6. Evaluation of Optical Diffusion Characteristics

The optical diffusion characteristics of the optical diffusion film thusobtained were evaluated.

Namely, a pressure-sensitive adhesive layer was provided on the surfaceof the release film of the optical diffusion film obtained in a state ofbeing interposed between a PET film and a release film, and the opticaldiffusion film was adhered to a soda lime glass having a thickness of1.1 mm. This was used as a specimen for evaluation.

Next, light was caused to enter into the optical diffusion film throughthe glass side of the specimen, that is, through the second internalstructure side, as illustrated in FIG. 9, using a conoscope(manufactured by autronic-MELCHERS GmbH), while the incident angle θ2(°) was varied to 0°, 10°, 20°, 30°, 40°, 50°, and 60°. The conoscopicimages thus obtained are presented in FIGS. 10(a) to 10(g).

From the results, since diffusion of the incident light occurred even ina case in which the incident angle θ2 of the incident light was variedfrom 0° to 60°, it is understood that the optical diffusion film has awide optical diffusion incident angle region including at least from 0°to 60°.

Furthermore, although there is variation in the shape or intensitydistribution of diffused light depending on the incident angle,crescent-shaped diffusion with an extremely narrow width orcircular-shaped diffusion with an extremely small radius, whichindicates that diffusion is insufficient, does not occur. Therefore, itis understood that changes in the optical diffusion characteristics areeffectively suppressed.

Example 2

In Example 2, an optical diffusion film was manufactured in the samemanner as in Example 1, except that when the composition for an opticaldiffusion film was manufactured, the type of the ultraviolet absorber asthe component (D) was changed to TINUVIN 477 manufactured by BASF SE,which is a mixed product of hydroxyphenyltriazine-based ultravioletabsorbers, the amount of addition thereof was changed to 0.1 parts byweight relative to 100 parts by weight in total of the component (A) andthe component (B), and the film thickness of the optical diffusion filmwas changed to 194 μm. The results thus obtained are presented in FIGS.11(a) and 11(b).

FIG. 11(a) is a schematic diagram of a cross-section obtained by cuttingthe optical diffusion film thus obtained, at a plane that was parallelto the direction of movement of the coating layer and orthogonallyintersected the film plane. FIG. 11(b) is a photograph of thecross-section.

Furthermore, as illustrated in FIG. 11(a), the length L1 of the firstcolumnar structure was 144.7 μm, and in the first columnar structure assuch, the length La of the portion upper than the bent section was 43.5μm, while the angle of inclination θa was 15°.

In the first columnar structure, the length Lb of the portion lower thanthe bent section was 101.2 μm, and the angle of inclination θb was 37°.

The absolute value of θb−θa was 22°.

Furthermore, the length L2 of the second columnar structure was 72 μm,and the angle of inclination θc was 0°.

Moreover, there existed an overlapping columnar structure (overlappinginternal structure) in which the tips of pillar-shaped objectsoriginating from the second columnar structure were brought into contactwith the vicinity of the tips of pillar-shaped objects originating fromthe first columnar structure, and the length L3 was 22.7 μm.

The absolute value of θa−θc in the overlapping internal structure was15°.

The optical diffusion characteristics of the optical diffusion film thusobtained were evaluated in the same manner as in Example 1. Conoscopicimages thus obtained are presented in FIGS. 12(a) to 12(g).

From the results, since diffusion of the incident light occurred even ina case in which the incident angle θ2 of the incident light was variedfrom 0° to 60°, it is understood that the optical diffusion film has awide optical diffusion incident angle region including at least from 0°to 60°.

Furthermore, although there is variation in the shape or intensitydistribution of diffused light depending on the incident angle,crescent-shaped diffusion with an extremely narrow width orcircular-shaped diffusion with an extremely small radius, whichindicates that diffusion is insufficient, does not occur. Therefore, itis understood that changes in the optical diffusion characteristics areeffectively suppressed.

Example 3

In Example 3, when the composition for an optical diffusion film wasmanufactured, the type of the ultraviolet absorber as the component (D)was changed to TINUVIN 477 manufactured by BASF SE, which is a mixedproduct of hydroxyphenyltriazine-based ultraviolet absorbers, the amountof addition of the ultraviolet absorber was set to 0.1 parts by weightrelative to 100 parts by weight in total of the component (A) and thecomponent (B), and the film thickness of the optical diffusion film wasadjusted to 190 μm.

As the first ultraviolet irradiation, as illustrated in FIG. 6(c), alinear light source 125 was used, and the coating layer 1 was irradiatedwith light that was substantially parallel light when viewed from theaxial direction of the linear light source 125 but appeared asnon-parallel random light 70′ when viewed from another direction, suchthat the angle of irradiation θ1 as illustrated in FIG. 7 would bealmost 20°.

The peak illuminance at that time was 21.95 mW/cm², the cumulativeamount of light was 24.65 mJ/cm², the lamp height was 500 mm, and thespeed of movement of the coating layer was 0.2 m/min.

Also, after the first ultraviolet irradiation process was completed, arelease film having ultraviolet transmissibility (manufactured by LintecCorp., SP-PET382050) and having a thickness of 38 μm was laminated onthe exposed surface side of the coating layer, and the resultant wassubjected to a non-oxygen atmosphere.

Next, as the second ultraviolet irradiation, similarly to the firstultraviolet irradiation process, the coating layer was irradiated usinga linear light source, such that the angle of inclination θ1 asillustrated in FIG. 7 would be almost 0°.

The peak illuminance at that time was 1.24 mW/cm², the cumulative amountof light was 44.35 mJ/cm², the lamp height was 500 mm, and the speed ofmovement of the coating layer was 0.2 m/min.

Except for these, an optical diffusion film was manufactured in the samemanner as in Example 1. The results thus obtained are presented in FIGS.13(a) and 13(b).

FIG. 13(a) is a schematic diagram of a cross-section obtained by cuttingthe optical diffusion film thus obtained, at a plane that is parallel tothe direction of movement of the coating layer and orthogonallyintersects the film plane, and FIG. 13(b) is a photograph of thecross-section of the optical diffusion film.

Furthermore, as illustrated in FIG. 13(a), the length L1 of the firstlouver structure was 148 μm, and in the first louver structure as such,the length La of the portion upper than the bent section was 51.2 μm,while the angle of inclination θa was 11°.

In the first louver structure, the length Lb of the portion lower thanthe bent section was 96.8 μm, and the angle of inclination θb was 24°.

The absolute value of θb−θa was 13°.

The length L of the second louver structure was 62.4 μm, and the angleof inclination θc was 0°.

Moreover, there existed an overlapping louver structure (overlappinginternal structure) in which the tips of high refractive indexplate-shaped regions originating from the second louver structure werebrought into contact with the vicinity of the tips of high refractiveindex plate-shaped objects originating from the first louver structure,and the length L3 was 20.4 μm.

The absolute value of θa−θc in the overlapping internal structure was11°.

The optical diffusion characteristics of the optical diffusion film thusobtained were evaluated in the same manner as in Example 1, except thatincident light was caused to enter the optical diffusion film throughthe first internal structure side as illustrated in FIG. 9(b).Conoscopic images thus obtained are presented in FIGS. 14(a) to 14(g).

From the results, since diffusion of the incident light occurred even ina case in which the incident angle θ2 of the incident light was variedfrom 0° to 40°, it is understood that the optical diffusion film has awide optical diffusion incident angle region including at least from 0°to 40°.

Furthermore, although there is variation in the shape or intensitydistribution of diffused light depending on the incident angle,point-like diffusion which indicates that diffusion is insufficient andincident light is almost transmitted, does not occur. Therefore, it isunderstood that changes in the optical diffusion characteristics areeffectively suppressed.

Comparative Example 1

In Comparative Example 1, an optical diffusion film was manufactured inthe same manner as in Example 1, except that when the composition for anoptical diffusion film was manufactured, an ultraviolet absorber as thecomponent (D) was not added, and the film thickness of the opticaldiffusion film was adjusted to 198 μm. The results thus obtained arepresented in FIGS. 15(a) and 15(b).

FIG. 15(a) is a schematic diagram of a cross-section obtained by cuttingthe optical diffusion film thus obtained, at a plane that was parallelto the direction of movement of the coating layer and orthogonallyintersected the film plane. FIG. 15(b) is a photograph of thecross-section.

As illustrated in FIG. 15(a), the length L1 of the first columnarstructure was 143 μm, and the angle of inclination θa was 19°.Meanwhile, the pillar-shaped objects that constituted such a firstcolumnar structure did not have a bent section.

Furthermore, the length L2 of the second columnar structure was 69.8 μm,and the angle of inclination θc was 0°.

Moreover, there existed an overlapping columnar structure (overlappinginternal structure) in which the tips of pillar-shaped objectsoriginating from the second columnar structure were brought into contactwith the vicinity of the tips of pillar-shaped objects originating fromthe first columnar structure, and the length L3 was 14.8 μm.

The absolute value of θa−θc in the overlapping internal structure was19°.

The optical diffusion characteristics of the optical diffusion film thusobtained were evaluated in the same manner as in Example 1. Conoscopicimages thus obtained are presented in FIGS. 16(a) to 16(g).

From the results, since diffusion of the incident light occurred even ina case in which the incident angle θ2 of the incident light was variedfrom 0° to 60°, it is understood that the optical diffusion film has awide optical diffusion incident angle region including at least from 0°to 60°.

However, the shape or intensity distribution of the diffused lightnoticeably varied depending on the incident angle, and for example, whenθ2 was 50° or 60°, crescent-shaped diffusion with a fine width orring-shaped diffusion occurred, or when θ2 was 20° or 30°,circular-shaped diffusion with a small radius occurred.

Therefore, it is understood that changes in the optical diffusioncharacteristics associated with variation in the incident angle may notbe effectively suppressed.

Comparative Example 2

In Comparative Example 2, an optical diffusion film was manufactured inthe same manner as in Example 1, except that when the composition for anoptical diffusion film was manufactured, an ultraviolet absorber as thecomponent (D) was not added, the angle of irradiation θ1 as illustratedin FIG. 7 for the first irradiation with ultraviolet radiation wasalmost 40°, the peak illuminance was 1.26 mW/cm², and the cumulativeamount of light was 31.7 mJ/cm². The results thus obtained are presentedin FIGS. 17(a) and 17(b).

FIG. 17(a) is a schematic diagram of a cross-section obtained by cuttingthe optical diffusion film thus obtained, at a plane that was parallelto the direction of movement of the coating layer and orthogonallyintersected the film plane, and FIG. 17(b) is a photograph of thecross-section.

As illustrated in FIG. 17(a), the length L1 of the first columnarstructure was 145.6 μm, and the angle of inclination θa was 31°.Meanwhile, the pillar-shaped objects that constituted such a firstcolumnar structure did not have a bent section.

Furthermore, the length L2 of the second columnar structure was 67.6 μm,and the angle of inclination θc was 0°.

Moreover, there existed an overlapping columnar structure (overlappinginternal structure) in which the tips of pillar-shaped objectsoriginating from the second columnar structure were brought into contactwith the vicinity of the tips of pillar-shaped objects originating fromthe first columnar structure, and the length L3 was 15.2 μm.

The absolute value of θa−θc in the overlapping internal structure was31°.

The optical diffusion characteristics of the optical diffusion film thusobtained were evaluated in the same manner as in Example 1. Conoscopicimages thus obtained are presented in FIGS. 18(a) to 18(g).

From the results, since diffusion of the incident light occurred even ina case in which the incident angle θ2 of the incident light was variedfrom 0° to 60°, it is understood that the optical diffusion film has awide optical diffusion incident angle region including at least from 0°to 60°.

However, the shape or intensity distribution of the diffused lightnoticeably varied depending on the incident angle, and for example, whenθ2 was 30°, 40°, or 50°, circular-shaped diffusion with a small radiusoccurred.

Therefore, it is understood that changes in the optical diffusioncharacteristics associated with variation in the incident angle may notbe effectively suppressed.

Comparative Example 3

In Comparative Example 3, an optical diffusion film was manufactured inthe same manner as in Example 3, except that when a composition for anoptical diffusion film was manufactured, an ultraviolet absorber as thecomponent (D) was not added, and the film thickness of the opticaldiffusion film was adjusted to 196 μm. The results thus obtained arepresented in FIGS. 19(a) and 19(b).

FIG. 19(a) is a schematic diagram of a cross-section obtained by cuttingthe optical diffusion film thus obtained, at a plane that was parallelto the direction of movement of the coating layer and orthogonallyintersected the film plane, and FIG. 19(b) is a photograph of thecross-section.

As illustrated in FIG. 19(a), the length L1 of the first louverstructure was 143.6 μm, and the angle of inclination θa was 19°.Meanwhile, the high refractive index plate-shaped regions thatconstituted such a first louver structure did not have a bent section.

Furthermore, the length L2 of the second louver structure was 81.2 μm,and the angle of inclination θc was 0°.

Moreover, there existed an overlapping louver structure (overlappinginternal structure) in which the tips of high refractive indexplate-shaped regions originating from the second louver structure werebrought into contact with the vicinity of the tips of high refractiveindex plate-shaped regions originating from the first louver structure,and the length L3 was 28.8 μm.

The absolute value of θa−θc in the overlapping internal structure was19°.

The optical diffusion characteristics of the optical diffusion film thusobtained were evaluated in the same manner as in Example 3. Conoscopicimages thus obtained are presented in FIGS. 20(a) to 20(g).

From the results, since diffusion of the incident light occurred even ina case in which the incident angle θ2 of the incident light was variedfrom 0° to 40°, it is understood that the optical diffusion film has awide optical diffusion incident angle region including at least from 0°to 40°.

However, the intensity distribution of diffused light noticeably changesdepending on the incident angle, and for example, when θ2 was 30° or40°, diffused light is not observed from the film front.

Furthermore, diffusion occurring when θ2 was 0° was markedly decreased,and most of light was transmitted.

Therefore, it is understood that changes in the optical diffusioncharacteristics associated with variation in the incident angle may notbe effectively suppressed.

INDUSTRIAL APPLICABILITY

As described above, according to the invention, when a first internalstructure and a second internal structure are formed in a film, andalso, a bent section is provided in at least those regions having arelatively high refractive index, which constitute the first internalstructure, the optical diffusion incident angle region can beeffectively expanded, and even in a case in which the incident angle ofincident light is varied within the optical diffusion incident angleregion, changes in the optical diffusion characteristics can beeffectively suppressed.

Therefore, the optical diffusion film or the like of the invention canbe applied to a light control film in a refractive liquid crystaldisplay devices, as well as to a viewing angle control film, a viewingangle expanding film, and a projection screen, and is expected tosignificantly contribute to quality improvement of these products.

REFERENCE NUMERALS

-   -   1: Coating layer    -   2: Process sheet    -   10: Optical diffusion film    -   11: Low refractive index region    -   12: High refractive index region in first internal structure    -   12 a: Pillar-shaped object in first internal structure    -   12 b: High refractive index plate-shaped region in first        internal structure    -   12′: High refractive index region in second internal structure    -   12 a′: Pillar-shaped object in second internal structure    -   12 b′: High refractive index plate-shaped region in second        internal structure    -   14: Bent section    -   20: first internal structure    -   20 a: Columnar structure as first internal structure (bent        columnar structure)    -   20 b: Louver structure as first internal structure (bent louver        structure)    -   30: Second internal structure    -   30 a: Columnar structure as second internal structure    -   30 b: Louver structure as second internal structure    -   40: Overlapping internal structure    -   50: Optical diffusion layer    -   60: Parallel light    -   70: Light radiated from point light source    -   70′: Light radiated from linear light source    -   102: Point light source    -   104: Lens    -   125: Linear light source

What is claimed is:
 1. An optical diffusion film comprising, inside thefilm, a single optical diffusion layer having a first internal structureand a second internal structure, each of the internal structuresincluding a plurality of regions having a relatively high refractiveindex in a region having a relatively low refractive index, sequentiallyfrom the lower part along the film thickness direction, wherein thefirst internal structure and the second internal structure are bothlouver structure in which a plurality of plate-shaped regions havingdifferent refractive indices are alternately disposed in any onedirection along the film plane, wherein the regions having a relativelyhigh refractive index in the first internal structure have a bentsection at an intermediate point along the film thickness direction,wherein in the first internal structure, the angle of inclination θa,with respect to the normal line of the film plane, of the regions havinga relatively high refractive index in the portion upper than the bentsection is adjusted to a value within the range of 0° to 30°, and theangle of inclination θb, with respect to the normal line of the filmplane, of the regions having a relatively high refractive index in theportion lower than the bent section is adjusted to a value within therange of 1° to 60°, and wherein the absolute value of θb−θa is adjustedto a value within the range of 1° to 30° or less.
 2. The opticaldiffusion film according to claim 1, wherein in the first internalstructure, the length La of the regions having a relatively highrefractive index in the portion upper than the bent section is adjustedto a value within the range of 15 to 475 μm, and the length Lb of theregions having a relatively high refractive index in the portion lowerthan the bent section is adjusted to a value within the range of 15 to475 μm.
 3. The optical diffusion film according to claim 1, wherein theoptical diffusion film has an overlapping internal structure in whichthe position of the upper end of the first internal structure and theposition of the lower end of the second internal structure overlap witheach other in the film thickness direction.
 4. The optical diffusionfilm according to claim 3, wherein the overlapping internal structure isan overlapping internal structure in which the tips of the regionshaving a relatively high refractive index, which originate from any oneof the first internal structure and the second internal structure, arein contact with the vicinity of the tips of the regions having arelatively high refractive index, which originate from the otherinternal structure; or an overlapping internal structure in which theregions having a relatively high refractive index, which respectivelyoriginate from the first internal structure and the second internalstructure, overlap in a non-contact state.
 5. The optical diffusion filmaccording to claim 3, wherein the thickness of the overlapping internalstructure is adjusted to a value within the range of 1 to 40 μm.
 6. Amethod for manufacturing an optical diffusion film according to claim 1,the method comprising the following steps (a) to (d): (a) a step ofpreparing a composition for an optical diffusion film including at leasttwo polymerizable compounds having different refractive indices, aphotopolymerization initiator and an ultraviolet absorber, in which thecontent of the ultraviolet absorber is adjusted to a value of below 2parts by weight (provided that 0 parts by weight is excluded) relativeto the total amount (100 parts by weight) of the at least twopolymerizable compounds having different refractive indices; (b) a stepof applying the composition for an optical diffusion film on a processsheet, and forming a coating layer; (c) a step of subjecting the coatinglayer to first irradiation with active energy radiation to form a louverstructure as a first internal structure formed by bending anintermediate point along a film thickness of a region having arelatively high refractive index in the lower portion of the coatinglayer with the ultraviolet absorber, and also leaving a region where aninternal structure is not formed, in the upper portion of the coatinglayer; and (d) a step of subjecting the coating layer to secondirradiation with active energy radiation to form a louver structure as asecond internal structure in the region where an internal structure isnot formed.
 7. The method for manufacturing an optical diffusion filmaccording to claim 6, wherein the first irradiation with active energyradiation is performed in an oxygen-containing atmosphere, while thesecond irradiation with active energy radiation is performed in anon-oxygen atmosphere.
 8. An optical diffusion film comprising, insidethe film, a single optical diffusion layer having a first internalstructure and a second internal structure, each of the internalstructures including a plurality of regions having a relatively highrefractive index in a region having a relatively low refractive index,sequentially from the lower part along the film thickness direction,wherein the first internal structure is a louver structure in which aplurality of plate-shaped regions having different refractive indicesare alternately disposed in any one direction along the film plane,wherein the second internal structure is a columnar structure in which aplurality of pillar-shaped objects having a relatively high refractiveindex are arranged to stand close together in the film thicknessdirection in a region having a relatively low refractive index, whereinthe regions having a relatively high refractive index in the firstinternal structure have a bent section at an intermediate point alongthe film thickness direction, wherein in the first internal structure,the angle of inclination θa, with respect to the normal line of the filmplane, of the regions having a relatively high refractive index in theportion upper than the bent section is adjusted to a value within therange of 0° to 30°, and the angle of inclination θb, with respect to thenormal line of the film plane, of the regions having a relatively highrefractive index in the portion lower than the bent section is adjustedto a value within the range of 1° to 60°, and wherein the absolute valueof θb−θa is adjusted to a value within the range of 1° to 30° or less.9. A method for manufacturing an optical diffusion film according toclaim 8, the method comprising the following steps (a) to (d): (a) astep of preparing a composition for an optical diffusion film includingat least two polymerizable compounds having different refractiveindices, a photopolymerization initiator and an ultraviolet absorber, inwhich the content of the ultraviolet absorber is adjusted to a value ofbelow 2 parts by weight (provided that 0 parts by weight is excluded)relative to the total amount (100 parts by weight) of the at least twopolymerizable compounds having different refractive indices; (b) a stepof applying the composition for an optical diffusion film on a processsheet, and forming a coating layer; (c) a step of subjecting the coatinglayer to first irradiation with active energy radiation to form a louverstructure as a first internal structure formed by bending anintermediate point along a film thickness of a region having arelatively high refractive index in the lower portion of the coatinglayer with the ultraviolet absorber, and also leaving a region where aninternal structure is not formed, in the upper portion of the coatinglayer; and (d) a step of subjecting the coating layer to secondirradiation with active energy radiation to form a columnar structure asa second internal structure in the region where an internal structure isnot formed.
 10. The method for manufacturing an optical diffusion filmaccording to claim 9, wherein the first irradiation with active energyradiation is performed in an oxygen-containing atmosphere, while thesecond irradiation with active energy radiation is performed in anon-oxygen atmosphere.